[PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

This series contains a new patch from Sean added since v12 [1]:

* KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()

This frees up the function name kvm_is_error_gpa() such that it can then be
re-defined in:

* KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

to be used for a simple GPA validation helper function. The patch also now
contains an either/or address check for GPA versus HVA in
__kvm_gpc_refresh().

In:

* KVM: pfncache: add a mark-dirty helper

The function name has been changed from kvm_gpc_mark_dirty() to
kvm_gpc_mark_dirty_in_slot().

In:

* KVM: x86/xen: allow shared_info to be mapped by fixed HVA

missing HVA validation checks have been added and the 'hva == 0' test
has been changed to '!hva'. The KVM_XEN_ATTR_TYPE_SHARED_INFO and
KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA cases are still largely handled as one
though as separation leads to duplicate calls to
kvm_xen_shared_info_init() which looks messy.

Also, patches with a 'xen' prefix have now been modified to have a
'x86/xen' prefix and patches with a 'selftests / xen' prefix have been
modified to have simply a 'selftests' prefix.

[1] https://lore.kernel.org/kvm/20240115125707.1183-1-paul@xen.org/

David Woodhouse (1):
  KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

Paul Durrant (19):
  KVM: pfncache: Add a map helper function
  KVM: pfncache: remove unnecessary exports
  KVM: x86/xen: mark guest pages dirty with the pfncache lock held
  KVM: pfncache: add a mark-dirty helper
  KVM: pfncache: remove KVM_GUEST_USES_PFN usage
  KVM: pfncache: stop open-coding offset_in_page()
  KVM: pfncache: include page offset in uhva and use it consistently
  KVM: pfncache: allow a cache to be activated with a fixed (userspace)
    HVA
  KVM: x86/xen: separate initialization of shared_info cache and content
  KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is
    set
  KVM: x86/xen: allow shared_info to be mapped by fixed HVA
  KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
  KVM: selftests: map Xen's shared_info page using HVA rather than GFN
  KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
  KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA
    capability
  KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
  KVM: x86/xen: don't block on pfncache locks in
    kvm_xen_set_evtchn_fast()
  KVM: pfncache: check the need for invalidation under read lock first
  KVM: x86/xen: allow vcpu_info content to be 'safely' copied

Sean Christopherson (1):
  KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()

 Documentation/virt/kvm/api.rst                |  53 ++-
 arch/s390/kvm/diag.c                          |   2 +-
 arch/s390/kvm/gaccess.c                       |  14 +-
 arch/s390/kvm/kvm-s390.c                      |   4 +-
 arch/s390/kvm/priv.c                          |   4 +-
 arch/s390/kvm/sigp.c                          |   2 +-
 arch/x86/kvm/x86.c                            |   7 +-
 arch/x86/kvm/xen.c                            | 361 +++++++++++------
 include/linux/kvm_host.h                      |  49 ++-
 include/linux/kvm_types.h                     |   8 -
 include/uapi/linux/kvm.h                      |   9 +-
 .../selftests/kvm/x86_64/xen_shinfo_test.c    |  59 ++-
 virt/kvm/pfncache.c                           | 382 ++++++++++--------
 13 files changed, 591 insertions(+), 363 deletions(-)


base-commit: 7455665a3521aa7b56245c0a2810f748adc5fdd4
-- 
2.39.2

[PATCH v13 01/21] KVM: pfncache: Add a map helper function

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

There is a pfncache unmap helper but mapping is open-coded. Arguably this
is fine because mapping is done in only one place, hva_to_pfn_retry(), but
adding the helper does make that function more readable.

No functional change intended.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>

v8:
 - Re-work commit comment.
 - Fix CONFIG_HAS_IOMEM=n build.
---
 virt/kvm/pfncache.c | 47 ++++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 2d6aba677830..10842f1eeeae 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -96,17 +96,32 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 }
 EXPORT_SYMBOL_GPL(kvm_gpc_check);
 
-static void gpc_unmap_khva(kvm_pfn_t pfn, void *khva)
+static void *gpc_map(kvm_pfn_t pfn)
 {
-	/* Unmap the old pfn/page if it was mapped before. */
-	if (!is_error_noslot_pfn(pfn) && khva) {
-		if (pfn_valid(pfn))
-			kunmap(pfn_to_page(pfn));
+	if (pfn_valid(pfn))
+		return kmap(pfn_to_page(pfn));
+
 #ifdef CONFIG_HAS_IOMEM
-		else
-			memunmap(khva);
+	return memremap(pfn_to_hpa(pfn), PAGE_SIZE, MEMREMAP_WB);
+#else
+	return NULL;
 #endif
+}
+
+static void gpc_unmap(kvm_pfn_t pfn, void *khva)
+{
+	/* Unmap the old pfn/page if it was mapped before. */
+	if (is_error_noslot_pfn(pfn) || !khva)
+		return;
+
+	if (pfn_valid(pfn)) {
+		kunmap(pfn_to_page(pfn));
+		return;
 	}
+
+#ifdef CONFIG_HAS_IOMEM
+	memunmap(khva);
+#endif
 }
 
 static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_seq)
@@ -175,7 +190,7 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 			 * the existing mapping and didn't create a new one.
 			 */
 			if (new_khva != old_khva)
-				gpc_unmap_khva(new_pfn, new_khva);
+				gpc_unmap(new_pfn, new_khva);
 
 			kvm_release_pfn_clean(new_pfn);
 
@@ -193,15 +208,11 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 		 * too must be done outside of gpc->lock!
 		 */
 		if (gpc->usage & KVM_HOST_USES_PFN) {
-			if (new_pfn == gpc->pfn) {
+			if (new_pfn == gpc->pfn)
 				new_khva = old_khva;
-			} else if (pfn_valid(new_pfn)) {
-				new_khva = kmap(pfn_to_page(new_pfn));
-#ifdef CONFIG_HAS_IOMEM
-			} else {
-				new_khva = memremap(pfn_to_hpa(new_pfn), PAGE_SIZE, MEMREMAP_WB);
-#endif
-			}
+			else
+				new_khva = gpc_map(new_pfn);
+
 			if (!new_khva) {
 				kvm_release_pfn_clean(new_pfn);
 				goto out_error;
@@ -326,7 +337,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	mutex_unlock(&gpc->refresh_lock);
 
 	if (unmap_old)
-		gpc_unmap_khva(old_pfn, old_khva);
+		gpc_unmap(old_pfn, old_khva);
 
 	return ret;
 }
@@ -412,7 +423,7 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
 		list_del(&gpc->list);
 		spin_unlock(&kvm->gpc_lock);
 
-		gpc_unmap_khva(old_pfn, old_khva);
+		gpc_unmap(old_pfn, old_khva);
 	}
 }
 EXPORT_SYMBOL_GPL(kvm_gpc_deactivate);
-- 
2.39.2

[PATCH v13 02/21] KVM: pfncache: remove unnecessary exports

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

There is no need for the existing kvm_gpc_XXX() functions to be exported.
Clean up now before additional functions are added in subsequent patches.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>

v8:
 - New in this version.
---
 virt/kvm/pfncache.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 10842f1eeeae..f3571f44d9af 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -94,7 +94,6 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 
 	return true;
 }
-EXPORT_SYMBOL_GPL(kvm_gpc_check);
 
 static void *gpc_map(kvm_pfn_t pfn)
 {
@@ -346,7 +345,6 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 {
 	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
 }
-EXPORT_SYMBOL_GPL(kvm_gpc_refresh);
 
 void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
 		  struct kvm_vcpu *vcpu, enum pfn_cache_usage usage)
@@ -363,7 +361,6 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
 	gpc->pfn = KVM_PFN_ERR_FAULT;
 	gpc->uhva = KVM_HVA_ERR_BAD;
 }
-EXPORT_SYMBOL_GPL(kvm_gpc_init);
 
 int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
 {
@@ -388,7 +385,6 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
 	}
 	return __kvm_gpc_refresh(gpc, gpa, len);
 }
-EXPORT_SYMBOL_GPL(kvm_gpc_activate);
 
 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
 {
@@ -426,4 +422,3 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
 		gpc_unmap(old_pfn, old_khva);
 	}
 }
-EXPORT_SYMBOL_GPL(kvm_gpc_deactivate);
-- 
2.39.2

[PATCH v13 03/21] KVM: x86/xen: mark guest pages dirty with the pfncache lock held

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Sampling gpa and memslot from an unlocked pfncache may yield inconsistent
values so, since there is no problem with calling mark_page_dirty_in_slot()
with the pfncache lock held, relocate the calls in
kvm_xen_update_runstate_guest() and kvm_xen_inject_pending_events()
accordingly.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v8:
 - New in this version.
---
 arch/x86/kvm/xen.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 4b4e738c6f1b..f3327508ae41 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -452,14 +452,13 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
 		smp_wmb();
 	}
 
-	if (user_len2)
+	if (user_len2) {
+		mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
 		read_unlock(&gpc2->lock);
-
-	read_unlock_irqrestore(&gpc1->lock, flags);
+	}
 
 	mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
-	if (user_len2)
-		mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
+	read_unlock_irqrestore(&gpc1->lock, flags);
 }
 
 void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)
@@ -565,13 +564,13 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
 			     : "0" (evtchn_pending_sel32));
 		WRITE_ONCE(vi->evtchn_upcall_pending, 1);
 	}
+
+	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 	read_unlock_irqrestore(&gpc->lock, flags);
 
 	/* For the per-vCPU lapic vector, deliver it as MSI. */
 	if (v->arch.xen.upcall_vector)
 		kvm_xen_inject_vcpu_vector(v);
-
-	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 }
 
 int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
-- 
2.39.2

[PATCH v13 04/21] KVM: pfncache: add a mark-dirty helper

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

At the moment pages are marked dirty by open-coded calls to
mark_page_dirty_in_slot(), directly deferefencing the gpa and memslot
from the cache. After a subsequent patch these may not always be set
so add a helper now so that caller will protected from the need to know
about this detail.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org

v13:
 - s/kvm_gpc_mark_dirty/kvm_gpc_mark_dirty_in_slot
 - Add a check for a NULL memslot pointer

v8:
 - Make the helper a static inline.
---
 arch/x86/kvm/x86.c       |  2 +-
 arch/x86/kvm/xen.c       |  6 +++---
 include/linux/kvm_host.h | 13 +++++++++++++
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b66c45e7f6f8..16269430006f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3151,7 +3151,7 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
 
 	guest_hv_clock->version = ++vcpu->hv_clock.version;
 
-	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
+	kvm_gpc_mark_dirty_in_slot(gpc);
 	read_unlock_irqrestore(&gpc->lock, flags);
 
 	trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index f3327508ae41..2d001a9c6378 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -453,11 +453,11 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
 	}
 
 	if (user_len2) {
-		mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
+		kvm_gpc_mark_dirty_in_slot(gpc2);
 		read_unlock(&gpc2->lock);
 	}
 
-	mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
+	kvm_gpc_mark_dirty_in_slot(gpc1);
 	read_unlock_irqrestore(&gpc1->lock, flags);
 }
 
@@ -565,7 +565,7 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
 		WRITE_ONCE(vi->evtchn_upcall_pending, 1);
 	}
 
-	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
+	kvm_gpc_mark_dirty_in_slot(gpc);
 	read_unlock_irqrestore(&gpc->lock, flags);
 
 	/* For the per-vCPU lapic vector, deliver it as MSI. */
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index bbfefd7e612f..5a27b4389d32 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1398,6 +1398,19 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len);
  */
 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
 
+/**
+ * kvm_gpc_mark_dirty_in_slot - mark a cached guest page as dirty.
+ *
+ * @gpc:	   struct gfn_to_pfn_cache object.
+ */
+static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
+{
+	lockdep_assert_held(&gpc->lock);
+	if (gpc->memslot)
+		mark_page_dirty_in_slot(gpc->kvm, gpc->memslot,
+					gpc->gpa >> PAGE_SHIFT);
+}
+
 void kvm_sigset_activate(struct kvm_vcpu *vcpu);
 void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
 
-- 
2.39.2

Re: [PATCH v13 04/21] KVM: pfncache: add a mark-dirty helper

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> +/**
> + * kvm_gpc_mark_dirty_in_slot - mark a cached guest page as dirty.
> + *
> + * @gpc:	   struct gfn_to_pfn_cache object.

Meh, just omit the kerneldoc comment.  

> + */
> +static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
> +{
> +	lockdep_assert_held(&gpc->lock);
> +	if (gpc->memslot)
> +		mark_page_dirty_in_slot(gpc->kvm, gpc->memslot,
> +					gpc->gpa >> PAGE_SHIFT);

It's kinda silly, but I think it's worth landing this below gpa_to_gfn() so that
there's no need to open code the shift.

And I have a (very) slight preference for an early return.

static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
{
	lockdep_assert_held(&gpc->lock);

	if (!gpc->memslot)
		return;

	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpa_to_gfn(gpc->gpa));
}

> +}
> +
>  void kvm_sigset_activate(struct kvm_vcpu *vcpu);
>  void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
>  
> -- 
> 2.39.2
> 

Re: [PATCH v13 04/21] KVM: pfncache: add a mark-dirty helper

[Paul Durrant]

On 19/02/2024 21:42, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> +/**
>> + * kvm_gpc_mark_dirty_in_slot - mark a cached guest page as dirty.
>> + *
>> + * @gpc:	   struct gfn_to_pfn_cache object.
> 
> Meh, just omit the kerneldoc comment.
> 
>> + */
>> +static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
>> +{
>> +	lockdep_assert_held(&gpc->lock);
>> +	if (gpc->memslot)
>> +		mark_page_dirty_in_slot(gpc->kvm, gpc->memslot,
>> +					gpc->gpa >> PAGE_SHIFT);
> 
> It's kinda silly, but I think it's worth landing this below gpa_to_gfn() so that
> there's no need to open code the shift.
> 
> And I have a (very) slight preference for an early return.
> 
> static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
> {
> 	lockdep_assert_held(&gpc->lock);
> 
> 	if (!gpc->memslot)
> 		return;
> 
> 	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpa_to_gfn(gpc->gpa));
> }
> 

Ok. Will change.

>> +}
>> +
>>   void kvm_sigset_activate(struct kvm_vcpu *vcpu);
>>   void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
>>   
>> -- 
>> 2.39.2
>>

[PATCH v13 05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
callers of kvm_gpc_init(), which also makes the 'vcpu' argument redundant.
Moreover, all existing callers specify KVM_HOST_USES_PFN so the usage
check in hva_to_pfn_retry() and hence the 'usage' argument to
kvm_gpc_init() are also redundant.
Remove the pfn_cache_usage enumeration and remove the redundant arguments,
fields of struct gfn_to_hva_cache, and all the related code.

[1] https://lore.kernel.org/all/ZQiR8IpqOZrOpzHC@google.com/

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v8:
 - New in this version.
---
 arch/x86/kvm/x86.c        |  2 +-
 arch/x86/kvm/xen.c        | 14 ++++-----
 include/linux/kvm_host.h  | 11 +------
 include/linux/kvm_types.h |  8 -----
 virt/kvm/pfncache.c       | 61 ++++++---------------------------------
 5 files changed, 16 insertions(+), 80 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16269430006f..31cd5d803dae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12042,7 +12042,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	vcpu->arch.regs_avail = ~0;
 	vcpu->arch.regs_dirty = ~0;
 
-	kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm, vcpu, KVM_HOST_USES_PFN);
+	kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm);
 
 	if (!irqchip_in_kernel(vcpu->kvm) || kvm_vcpu_is_reset_bsp(vcpu))
 		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 2d001a9c6378..e90464225467 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -2108,14 +2108,10 @@ void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
 
 	timer_setup(&vcpu->arch.xen.poll_timer, cancel_evtchn_poll, 0);
 
-	kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
-	kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm, NULL,
-		     KVM_HOST_USES_PFN);
+	kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm);
+	kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm);
 }
 
 void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
@@ -2158,7 +2154,7 @@ void kvm_xen_init_vm(struct kvm *kvm)
 {
 	mutex_init(&kvm->arch.xen.xen_lock);
 	idr_init(&kvm->arch.xen.evtchn_ports);
-	kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm, NULL, KVM_HOST_USES_PFN);
+	kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm);
 }
 
 void kvm_xen_destroy_vm(struct kvm *kvm)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5a27b4389d32..da20b7018cc8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1318,21 +1318,12 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
  *
  * @gpc:	   struct gfn_to_pfn_cache object.
  * @kvm:	   pointer to kvm instance.
- * @vcpu:	   vCPU to be used for marking pages dirty and to be woken on
- *		   invalidation.
- * @usage:	   indicates if the resulting host physical PFN is used while
- *		   the @vcpu is IN_GUEST_MODE (in which case invalidation of 
- *		   the cache from MMU notifiers---but not for KVM memslot
- *		   changes!---will also force @vcpu to exit the guest and
- *		   refresh the cache); and/or if the PFN used directly
- *		   by KVM (and thus needs a kernel virtual mapping).
  *
  * This sets up a gfn_to_pfn_cache by initializing locks and assigning the
  * immutable attributes.  Note, the cache must be zero-allocated (or zeroed by
  * the caller before init).
  */
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
-		  struct kvm_vcpu *vcpu, enum pfn_cache_usage usage);
+void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
 
 /**
  * kvm_gpc_activate - prepare a cached kernel mapping and HPA for a given guest
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 9d1f7835d8c1..d93f6522b2c3 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -49,12 +49,6 @@ typedef u64            hfn_t;
 
 typedef hfn_t kvm_pfn_t;
 
-enum pfn_cache_usage {
-	KVM_GUEST_USES_PFN = BIT(0),
-	KVM_HOST_USES_PFN  = BIT(1),
-	KVM_GUEST_AND_HOST_USE_PFN = KVM_GUEST_USES_PFN | KVM_HOST_USES_PFN,
-};
-
 struct gfn_to_hva_cache {
 	u64 generation;
 	gpa_t gpa;
@@ -69,13 +63,11 @@ struct gfn_to_pfn_cache {
 	unsigned long uhva;
 	struct kvm_memory_slot *memslot;
 	struct kvm *kvm;
-	struct kvm_vcpu *vcpu;
 	struct list_head list;
 	rwlock_t lock;
 	struct mutex refresh_lock;
 	void *khva;
 	kvm_pfn_t pfn;
-	enum pfn_cache_usage usage;
 	bool active;
 	bool valid;
 };
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index f3571f44d9af..6f4b537eb25b 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -25,9 +25,7 @@
 void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
 				       unsigned long end, bool may_block)
 {
-	DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
 	struct gfn_to_pfn_cache *gpc;
-	bool evict_vcpus = false;
 
 	spin_lock(&kvm->gpc_lock);
 	list_for_each_entry(gpc, &kvm->gpc_list, list) {
@@ -37,43 +35,10 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
 		if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
 		    gpc->uhva >= start && gpc->uhva < end) {
 			gpc->valid = false;
-
-			/*
-			 * If a guest vCPU could be using the physical address,
-			 * it needs to be forced out of guest mode.
-			 */
-			if (gpc->usage & KVM_GUEST_USES_PFN) {
-				if (!evict_vcpus) {
-					evict_vcpus = true;
-					bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
-				}
-				__set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap);
-			}
 		}
 		write_unlock_irq(&gpc->lock);
 	}
 	spin_unlock(&kvm->gpc_lock);
-
-	if (evict_vcpus) {
-		/*
-		 * KVM needs to ensure the vCPU is fully out of guest context
-		 * before allowing the invalidation to continue.
-		 */
-		unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE;
-		bool called;
-
-		/*
-		 * If the OOM reaper is active, then all vCPUs should have
-		 * been stopped already, so perform the request without
-		 * KVM_REQUEST_WAIT and be sad if any needed to be IPI'd.
-		 */
-		if (!may_block)
-			req &= ~KVM_REQUEST_WAIT;
-
-		called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap);
-
-		WARN_ON_ONCE(called && !may_block);
-	}
 }
 
 bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
@@ -206,16 +171,14 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 		 * pfn.  Note, kmap() and memremap() can both sleep, so this
 		 * too must be done outside of gpc->lock!
 		 */
-		if (gpc->usage & KVM_HOST_USES_PFN) {
-			if (new_pfn == gpc->pfn)
-				new_khva = old_khva;
-			else
-				new_khva = gpc_map(new_pfn);
-
-			if (!new_khva) {
-				kvm_release_pfn_clean(new_pfn);
-				goto out_error;
-			}
+		if (new_pfn == gpc->pfn)
+			new_khva = old_khva;
+		else
+			new_khva = gpc_map(new_pfn);
+
+		if (!new_khva) {
+			kvm_release_pfn_clean(new_pfn);
+			goto out_error;
 		}
 
 		write_lock_irq(&gpc->lock);
@@ -346,18 +309,12 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
 }
 
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
-		  struct kvm_vcpu *vcpu, enum pfn_cache_usage usage)
+void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
 {
-	WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage);
-	WARN_ON_ONCE((usage & KVM_GUEST_USES_PFN) && !vcpu);
-
 	rwlock_init(&gpc->lock);
 	mutex_init(&gpc->refresh_lock);
 
 	gpc->kvm = kvm;
-	gpc->vcpu = vcpu;
-	gpc->usage = usage;
 	gpc->pfn = KVM_PFN_ERR_FAULT;
 	gpc->uhva = KVM_HVA_ERR_BAD;
 }
-- 
2.39.2

Re: [PATCH v13 05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@amazon.com>
> 
> As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
> callers of kvm_gpc_init(), which also makes the 'vcpu' argument redundant.

The changelog should explicitly call out that not only is KVM_GUEST_USES_PFN
unused, it's incomplete/broken (which is also partly why it's unused).  Without
that information, removing the support looks like a somewhat arbitrary decision,
versus a deliberate change to make it easier to support the gpc code.

Re: [PATCH v13 05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage

[Paul Durrant]

On 19/02/2024 21:43, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> From: Paul Durrant <pdurrant@amazon.com>
>>
>> As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
>> callers of kvm_gpc_init(), which also makes the 'vcpu' argument redundant.
> 
> The changelog should explicitly call out that not only is KVM_GUEST_USES_PFN
> unused, it's incomplete/broken (which is also partly why it's unused).  Without
> that information, removing the support looks like a somewhat arbitrary decision,
> versus a deliberate change to make it easier to support the gpc code.

Ok. I'll add some words to that effect.

[PATCH v13 06/21] KVM: pfncache: stop open-coding offset_in_page()

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Some code in pfncache uses offset_in_page() but in other places it is open-
coded. Use offset_in_page() consistently everywhere.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v8:
 - New in this version.
---
 virt/kvm/pfncache.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 6f4b537eb25b..0eeb034d0674 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -48,7 +48,7 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 	if (!gpc->active)
 		return false;
 
-	if ((gpc->gpa & ~PAGE_MASK) + len > PAGE_SIZE)
+	if (offset_in_page(gpc->gpa) + len > PAGE_SIZE)
 		return false;
 
 	if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
@@ -192,7 +192,7 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 
 	gpc->valid = true;
 	gpc->pfn = new_pfn;
-	gpc->khva = new_khva + (gpc->gpa & ~PAGE_MASK);
+	gpc->khva = new_khva + offset_in_page(gpc->gpa);
 
 	/*
 	 * Put the reference to the _new_ pfn.  The pfn is now tracked by the
@@ -213,7 +213,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 			     unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
-	unsigned long page_offset = gpa & ~PAGE_MASK;
+	unsigned long page_offset = offset_in_page(gpa);
 	bool unmap_old = false;
 	unsigned long old_uhva;
 	kvm_pfn_t old_pfn;
-- 
2.39.2

[PATCH v13 07/21] KVM: pfncache: include page offset in uhva and use it consistently

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Currently the pfncache page offset is sometimes determined using the gpa
and sometimes the khva, whilst the uhva is always page-aligned. After a
subsequent patch is applied the gpa will not always be valid so adjust
the code to include the page offset in the uhva and use it consistently
as the source of truth.

Also, where a page-aligned address is required, use PAGE_ALIGN_DOWN()
for clarity.

No functional change intended.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v8:
 - New in this version.
---
 virt/kvm/pfncache.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 0eeb034d0674..97eec8ee3449 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -48,10 +48,10 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 	if (!gpc->active)
 		return false;
 
-	if (offset_in_page(gpc->gpa) + len > PAGE_SIZE)
+	if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
 		return false;
 
-	if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
+	if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
 		return false;
 
 	if (!gpc->valid)
@@ -119,7 +119,7 @@ static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_s
 static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 {
 	/* Note, the new page offset may be different than the old! */
-	void *old_khva = gpc->khva - offset_in_page(gpc->khva);
+	void *old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
 	void *new_khva = NULL;
 	unsigned long mmu_seq;
@@ -192,7 +192,7 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 
 	gpc->valid = true;
 	gpc->pfn = new_pfn;
-	gpc->khva = new_khva + offset_in_page(gpc->gpa);
+	gpc->khva = new_khva + offset_in_page(gpc->uhva);
 
 	/*
 	 * Put the reference to the _new_ pfn.  The pfn is now tracked by the
@@ -217,6 +217,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	bool unmap_old = false;
 	unsigned long old_uhva;
 	kvm_pfn_t old_pfn;
+	bool hva_change = false;
 	void *old_khva;
 	int ret;
 
@@ -242,10 +243,10 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	}
 
 	old_pfn = gpc->pfn;
-	old_khva = gpc->khva - offset_in_page(gpc->khva);
-	old_uhva = gpc->uhva;
+	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
+	old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);
 
-	/* If the userspace HVA is invalid, refresh that first */
+	/* Refresh the userspace HVA if necessary */
 	if (gpc->gpa != gpa || gpc->generation != slots->generation ||
 	    kvm_is_error_hva(gpc->uhva)) {
 		gfn_t gfn = gpa_to_gfn(gpa);
@@ -259,13 +260,25 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 			ret = -EFAULT;
 			goto out;
 		}
+
+		/*
+		 * Even if the GPA and/or the memslot generation changed, the
+		 * HVA may still be the same.
+		 */
+		if (gpc->uhva != old_uhva)
+			hva_change = true;
+	} else {
+		gpc->uhva = old_uhva;
 	}
 
+	/* Note: the offset must be correct before calling hva_to_pfn_retry() */
+	gpc->uhva += page_offset;
+
 	/*
 	 * If the userspace HVA changed or the PFN was already invalid,
 	 * drop the lock and do the HVA to PFN lookup again.
 	 */
-	if (!gpc->valid || old_uhva != gpc->uhva) {
+	if (!gpc->valid || hva_change) {
 		ret = hva_to_pfn_retry(gpc);
 	} else {
 		/*
-- 
2.39.2

[PATCH v13 08/21] KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()

[Paul Durrant]

From: Sean Christopherson <seanjc@google.com>

Rename kvm_is_error_gpa() to kvm_is_gpa_in_memslot() and invert the
polarity accordingly in order to (a) free up kvm_is_error_gpa() to match
with kvm_is_error_{hva,page}(), and (b) to make it more obvious that the
helper is doing a memslot lookup, i.e. not simply checking for INVALID_GPA.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-s390@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

v13:
 - New in this version.
---
 arch/s390/kvm/diag.c     |  2 +-
 arch/s390/kvm/gaccess.c  | 14 +++++++-------
 arch/s390/kvm/kvm-s390.c |  4 ++--
 arch/s390/kvm/priv.c     |  4 ++--
 arch/s390/kvm/sigp.c     |  2 +-
 include/linux/kvm_host.h |  4 ++--
 6 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index 3c65b8258ae6..2a32438e09ce 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -102,7 +102,7 @@ static int __diag_page_ref_service(struct kvm_vcpu *vcpu)
 		    parm.token_addr & 7 || parm.zarch != 0x8000000000000000ULL)
 			return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
-		if (kvm_is_error_gpa(vcpu->kvm, parm.token_addr))
+		if (!kvm_is_gpa_in_memslot(vcpu->kvm, parm.token_addr))
 			return kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
 
 		vcpu->arch.pfault_token = parm.token_addr;
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 5bfcc50c1a68..415c99649e43 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -664,7 +664,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 	case ASCE_TYPE_REGION1:	{
 		union region1_table_entry rfte;
 
-		if (kvm_is_error_gpa(vcpu->kvm, ptr))
+		if (!kvm_is_gpa_in_memslot(vcpu->kvm, ptr))
 			return PGM_ADDRESSING;
 		if (deref_table(vcpu->kvm, ptr, &rfte.val))
 			return -EFAULT;
@@ -682,7 +682,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 	case ASCE_TYPE_REGION2: {
 		union region2_table_entry rste;
 
-		if (kvm_is_error_gpa(vcpu->kvm, ptr))
+		if (!kvm_is_gpa_in_memslot(vcpu->kvm, ptr))
 			return PGM_ADDRESSING;
 		if (deref_table(vcpu->kvm, ptr, &rste.val))
 			return -EFAULT;
@@ -700,7 +700,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 	case ASCE_TYPE_REGION3: {
 		union region3_table_entry rtte;
 
-		if (kvm_is_error_gpa(vcpu->kvm, ptr))
+		if (!kvm_is_gpa_in_memslot(vcpu->kvm, ptr))
 			return PGM_ADDRESSING;
 		if (deref_table(vcpu->kvm, ptr, &rtte.val))
 			return -EFAULT;
@@ -728,7 +728,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 	case ASCE_TYPE_SEGMENT: {
 		union segment_table_entry ste;
 
-		if (kvm_is_error_gpa(vcpu->kvm, ptr))
+		if (!kvm_is_gpa_in_memslot(vcpu->kvm, ptr))
 			return PGM_ADDRESSING;
 		if (deref_table(vcpu->kvm, ptr, &ste.val))
 			return -EFAULT;
@@ -748,7 +748,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 		ptr = ste.fc0.pto * (PAGE_SIZE / 2) + vaddr.px * 8;
 	}
 	}
-	if (kvm_is_error_gpa(vcpu->kvm, ptr))
+	if (!kvm_is_gpa_in_memslot(vcpu->kvm, ptr))
 		return PGM_ADDRESSING;
 	if (deref_table(vcpu->kvm, ptr, &pte.val))
 		return -EFAULT;
@@ -770,7 +770,7 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
 		*prot = PROT_TYPE_IEP;
 		return PGM_PROTECTION;
 	}
-	if (kvm_is_error_gpa(vcpu->kvm, raddr.addr))
+	if (!kvm_is_gpa_in_memslot(vcpu->kvm, raddr.addr))
 		return PGM_ADDRESSING;
 	*gpa = raddr.addr;
 	return 0;
@@ -957,7 +957,7 @@ static int guest_range_to_gpas(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
 				return rc;
 		} else {
 			gpa = kvm_s390_real_to_abs(vcpu, ga);
-			if (kvm_is_error_gpa(vcpu->kvm, gpa)) {
+			if (!kvm_is_gpa_in_memslot(vcpu->kvm, gpa)) {
 				rc = PGM_ADDRESSING;
 				prot = PROT_NONE;
 			}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ea63ac769889..3e5a1d7aa81a 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2878,7 +2878,7 @@ static int kvm_s390_vm_mem_op_abs(struct kvm *kvm, struct kvm_s390_mem_op *mop)
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 
-	if (kvm_is_error_gpa(kvm, mop->gaddr)) {
+	if (!kvm_is_gpa_in_memslot(kvm, mop->gaddr)) {
 		r = PGM_ADDRESSING;
 		goto out_unlock;
 	}
@@ -2940,7 +2940,7 @@ static int kvm_s390_vm_mem_op_cmpxchg(struct kvm *kvm, struct kvm_s390_mem_op *m
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 
-	if (kvm_is_error_gpa(kvm, mop->gaddr)) {
+	if (!kvm_is_gpa_in_memslot(kvm, mop->gaddr)) {
 		r = PGM_ADDRESSING;
 		goto out_unlock;
 	}
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 621a17fd1a1b..0ece9c581ebf 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -149,7 +149,7 @@ static int handle_set_prefix(struct kvm_vcpu *vcpu)
 	 * first page, since address is 8k aligned and memory pieces are always
 	 * at least 1MB aligned and have at least a size of 1MB.
 	 */
-	if (kvm_is_error_gpa(vcpu->kvm, address))
+	if (!kvm_is_gpa_in_memslot(vcpu->kvm, address))
 		return kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
 
 	kvm_s390_set_prefix(vcpu, address);
@@ -464,7 +464,7 @@ static int handle_test_block(struct kvm_vcpu *vcpu)
 		return kvm_s390_inject_prog_irq(vcpu, &vcpu->arch.pgm);
 	addr = kvm_s390_real_to_abs(vcpu, addr);
 
-	if (kvm_is_error_gpa(vcpu->kvm, addr))
+	if (!kvm_is_gpa_in_memslot(vcpu->kvm, addr))
 		return kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
 	/*
 	 * We don't expect errors on modern systems, and do not care
diff --git a/arch/s390/kvm/sigp.c b/arch/s390/kvm/sigp.c
index d9696b530064..55c34cb35428 100644
--- a/arch/s390/kvm/sigp.c
+++ b/arch/s390/kvm/sigp.c
@@ -172,7 +172,7 @@ static int __sigp_set_prefix(struct kvm_vcpu *vcpu, struct kvm_vcpu *dst_vcpu,
 	 * first page, since address is 8k aligned and memory pieces are always
 	 * at least 1MB aligned and have at least a size of 1MB.
 	 */
-	if (kvm_is_error_gpa(vcpu->kvm, irq.u.prefix.address)) {
+	if (!kvm_is_gpa_in_memslot(vcpu->kvm, irq.u.prefix.address)) {
 		*reg &= 0xffffffff00000000UL;
 		*reg |= SIGP_STATUS_INVALID_PARAMETER;
 		return SIGP_CC_STATUS_STORED;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index da20b7018cc8..41ee515b304e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1791,11 +1791,11 @@ static inline hpa_t pfn_to_hpa(kvm_pfn_t pfn)
 	return (hpa_t)pfn << PAGE_SHIFT;
 }
 
-static inline bool kvm_is_error_gpa(struct kvm *kvm, gpa_t gpa)
+static inline bool kvm_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa)
 {
 	unsigned long hva = gfn_to_hva(kvm, gpa_to_gfn(gpa));
 
-	return kvm_is_error_hva(hva);
+	return !kvm_is_error_hva(hva);
 }
 
 enum kvm_stat_kind {
-- 
2.39.2

[PATCH v13 09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Some pfncache pages may actually be overlays on guest memory that have a
fixed HVA within the VMM. It's pointless to invalidate such cached
mappings if the overlay is moved so allow a cache to be activated directly
with the HVA to cater for such cases. A subsequent patch will make use
of this facility.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v13:
 - Define kvm_is_error_gpa() to check GPA validity.
 - Add an either/or address check to __kvm_gpc_refresh() as requested.
 - Make sure memslot is NULL if the cache is activated with an HVA.

v11:
 - Fixed kvm_gpc_check() to ignore memslot generation if the cache is not
   activated with a GPA. (This breakage occured during the re-work for v8).

v9:
 - Pass both GPA and HVA into __kvm_gpc_refresh() rather than overloading
   the address paraneter and using a bool flag to indicated what it is.

v8:
 - Re-worked to avoid messing with struct gfn_to_pfn_cache.
---
 include/linux/kvm_host.h | 21 +++++++++
 virt/kvm/pfncache.c      | 94 +++++++++++++++++++++++++++++-----------
 2 files changed, 89 insertions(+), 26 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 41ee515b304e..043cc824d55a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -148,6 +148,11 @@ static inline bool kvm_is_error_hva(unsigned long addr)
 
 #endif
 
+static inline bool kvm_is_error_gpa(gpa_t gpa)
+{
+	return gpa == INVALID_GPA;
+}
+
 #define KVM_ERR_PTR_BAD_PAGE	(ERR_PTR(-ENOENT))
 
 static inline bool is_error_page(struct page *page)
@@ -1343,6 +1348,22 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
  */
 int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
 
+/**
+ * kvm_gpc_activate_hva - prepare a cached kernel mapping and HPA for a given HVA.
+ *
+ * @gpc:          struct gfn_to_pfn_cache object.
+ * @hva:          userspace virtual address to map.
+ * @len:          sanity check; the range being access must fit a single page.
+ *
+ * @return:       0 for success.
+ *                -EINVAL for a mapping which would cross a page boundary.
+ *                -EFAULT for an untranslatable guest physical address.
+ *
+ * The semantics of this function are the same as those of kvm_gpc_activate(). It
+ * merely bypasses a layer of address translation.
+ */
+int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long hva, unsigned long len);
+
 /**
  * kvm_gpc_check - check validity of a gfn_to_pfn_cache.
  *
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 97eec8ee3449..4e64d349b2f7 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -48,7 +48,14 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 	if (!gpc->active)
 		return false;
 
-	if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
+	/*
+	 * If the page was cached from a memslot, make sure the memslots have
+	 * not been re-configured.
+	 */
+	if (!kvm_is_error_gpa(gpc->gpa) && gpc->generation != slots->generation)
+		return false;
+
+	if (kvm_is_error_hva(gpc->uhva))
 		return false;
 
 	if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
@@ -209,11 +216,11 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 	return -EFAULT;
 }
 
-static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
+static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
 			     unsigned long len)
 {
-	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
-	unsigned long page_offset = offset_in_page(gpa);
+	unsigned long page_offset = kvm_is_error_gpa(gpa) ?
+		offset_in_page(uhva) : offset_in_page(gpa);
 	bool unmap_old = false;
 	unsigned long old_uhva;
 	kvm_pfn_t old_pfn;
@@ -221,6 +228,10 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	void *old_khva;
 	int ret;
 
+	/* Either gpa or uhva must be valid, but not both */
+	if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva)))
+		return -EINVAL;
+
 	/*
 	 * If must fit within a single page. The 'len' argument is
 	 * only to enforce that.
@@ -246,29 +257,39 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);
 
-	/* Refresh the userspace HVA if necessary */
-	if (gpc->gpa != gpa || gpc->generation != slots->generation ||
-	    kvm_is_error_hva(gpc->uhva)) {
-		gfn_t gfn = gpa_to_gfn(gpa);
-
-		gpc->gpa = gpa;
-		gpc->generation = slots->generation;
-		gpc->memslot = __gfn_to_memslot(slots, gfn);
-		gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
+	if (kvm_is_error_gpa(gpa)) {
+		gpc->gpa = INVALID_GPA;
+		gpc->memslot = NULL;
+		gpc->uhva = PAGE_ALIGN_DOWN(uhva);
 
-		if (kvm_is_error_hva(gpc->uhva)) {
-			ret = -EFAULT;
-			goto out;
-		}
-
-		/*
-		 * Even if the GPA and/or the memslot generation changed, the
-		 * HVA may still be the same.
-		 */
 		if (gpc->uhva != old_uhva)
 			hva_change = true;
 	} else {
-		gpc->uhva = old_uhva;
+		struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
+
+		if (gpc->gpa != gpa || gpc->generation != slots->generation ||
+		    kvm_is_error_hva(gpc->uhva)) {
+			gfn_t gfn = gpa_to_gfn(gpa);
+
+			gpc->gpa = gpa;
+			gpc->generation = slots->generation;
+			gpc->memslot = __gfn_to_memslot(slots, gfn);
+			gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
+
+			if (kvm_is_error_hva(gpc->uhva)) {
+				ret = -EFAULT;
+				goto out;
+			}
+
+			/*
+			 * Even if the GPA and/or the memslot generation changed, the
+			 * HVA may still be the same.
+			 */
+			if (gpc->uhva != old_uhva)
+				hva_change = true;
+		} else {
+			gpc->uhva = old_uhva;
+		}
 	}
 
 	/* Note: the offset must be correct before calling hva_to_pfn_retry() */
@@ -319,7 +340,16 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 
 int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 {
-	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
+	unsigned long uhva = gpc->uhva;
+
+	/*
+	 * If the GPA is valid then invalidate the HVA, otherwise
+	 * __kvm_gpc_refresh() will fail its strict either/or address check.
+	 */
+	if (!kvm_is_error_gpa(gpc->gpa))
+		uhva = KVM_HVA_ERR_BAD;
+
+	return __kvm_gpc_refresh(gpc, gpc->gpa, uhva, len);
 }
 
 void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
@@ -329,10 +359,12 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
 
 	gpc->kvm = kvm;
 	gpc->pfn = KVM_PFN_ERR_FAULT;
+	gpc->gpa = INVALID_GPA;
 	gpc->uhva = KVM_HVA_ERR_BAD;
 }
 
-int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
+static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
+			      unsigned long len)
 {
 	struct kvm *kvm = gpc->kvm;
 
@@ -353,7 +385,17 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
 		gpc->active = true;
 		write_unlock_irq(&gpc->lock);
 	}
-	return __kvm_gpc_refresh(gpc, gpa, len);
+	return __kvm_gpc_refresh(gpc, gpa, uhva, len);
+}
+
+int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
+}
+
+int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len);
 }
 
 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
-- 
2.39.2

Re: [PATCH v13 09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> @@ -319,7 +340,16 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>  
>  int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
>  {
> -	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
> +	unsigned long uhva = gpc->uhva;
> +
> +	/*
> +	 * If the GPA is valid then invalidate the HVA, otherwise
> +	 * __kvm_gpc_refresh() will fail its strict either/or address check.
> +	 */

It's not just to make the strict check happy, though that's obviously the direct
motivation, it's so that there's one root of truth.  The strict check is there to
enforce that behavior and to make it  more clear to readers that it's an either/or
situation.

> +	if (!kvm_is_error_gpa(gpc->gpa))
> +		uhva = KVM_HVA_ERR_BAD;

This would be a good time to use a ternary operator.

	/*
	 * If the GPA is valid then ignore the HVA, as a cache can be GPA-based
	 * or HVA-based, not both.  For GPA-based caches, the HVA will be
	 * recomputed during refresh if necessary.
	 */
	unsigned long uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva :
							  KVM_HVA_ERR_BAD;

Re: [PATCH v13 09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

[Paul Durrant]

On 19/02/2024 21:49, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> @@ -319,7 +340,16 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>>   
>>   int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
>>   {
>> -	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
>> +	unsigned long uhva = gpc->uhva;
>> +
>> +	/*
>> +	 * If the GPA is valid then invalidate the HVA, otherwise
>> +	 * __kvm_gpc_refresh() will fail its strict either/or address check.
>> +	 */
> 
> It's not just to make the strict check happy, though that's obviously the direct
> motivation, it's so that there's one root of truth.  The strict check is there to
> enforce that behavior and to make it  more clear to readers that it's an either/or
> situation.
> 
>> +	if (!kvm_is_error_gpa(gpc->gpa))
>> +		uhva = KVM_HVA_ERR_BAD;
> 
> This would be a good time to use a ternary operator.
> 
> 	/*
> 	 * If the GPA is valid then ignore the HVA, as a cache can be GPA-based
> 	 * or HVA-based, not both.  For GPA-based caches, the HVA will be
> 	 * recomputed during refresh if necessary.
> 	 */
> 	unsigned long uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva :
> 							  KVM_HVA_ERR_BAD;

Ok. I thought that actually looked a little less neat in this case, but 
I'll change.

[PATCH v13 10/21] KVM: x86/xen: separate initialization of shared_info cache and content

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

A subsequent patch will allow shared_info to be initialized using either a
GPA or a user-space (i.e. VMM) HVA. To make that patch cleaner, separate
the initialization of the shared_info content from the activation of the
pfncache.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v11:
 - Fix accidental regression from commit 5d6d6a7d7e66a ("KVM: x86: Refine
   calculation of guest wall clock to use a single TSC read").

v10:
 - New in this version.
---
 arch/x86/kvm/xen.c | 55 +++++++++++++++++++++++++++-------------------
 1 file changed, 32 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index e90464225467..031e98d88ba2 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -34,41 +34,32 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r);
 
 DEFINE_STATIC_KEY_DEFERRED_FALSE(kvm_xen_enabled, HZ);
 
-static int kvm_xen_shared_info_init(struct kvm *kvm, gfn_t gfn)
+static int kvm_xen_shared_info_init(struct kvm *kvm)
 {
 	struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
 	struct pvclock_wall_clock *wc;
-	gpa_t gpa = gfn_to_gpa(gfn);
 	u32 *wc_sec_hi;
 	u32 wc_version;
 	u64 wall_nsec;
 	int ret = 0;
 	int idx = srcu_read_lock(&kvm->srcu);
 
-	if (gfn == KVM_XEN_INVALID_GFN) {
-		kvm_gpc_deactivate(gpc);
-		goto out;
-	}
+	read_lock_irq(&gpc->lock);
+	while (!kvm_gpc_check(gpc, PAGE_SIZE)) {
+		read_unlock_irq(&gpc->lock);
 
-	do {
-		ret = kvm_gpc_activate(gpc, gpa, PAGE_SIZE);
+		ret = kvm_gpc_refresh(gpc, PAGE_SIZE);
 		if (ret)
 			goto out;
 
-		/*
-		 * This code mirrors kvm_write_wall_clock() except that it writes
-		 * directly through the pfn cache and doesn't mark the page dirty.
-		 */
-		wall_nsec = kvm_get_wall_clock_epoch(kvm);
-
-		/* It could be invalid again already, so we need to check */
 		read_lock_irq(&gpc->lock);
+	}
 
-		if (gpc->valid)
-			break;
-
-		read_unlock_irq(&gpc->lock);
-	} while (1);
+	/*
+	 * This code mirrors kvm_write_wall_clock() except that it writes
+	 * directly through the pfn cache and doesn't mark the page dirty.
+	 */
+	wall_nsec = kvm_get_wall_clock_epoch(kvm);
 
 	/* Paranoia checks on the 32-bit struct layout */
 	BUILD_BUG_ON(offsetof(struct compat_shared_info, wc) != 0x900);
@@ -639,12 +630,30 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		}
 		break;
 
-	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
+		int idx;
+
 		mutex_lock(&kvm->arch.xen.xen_lock);
-		r = kvm_xen_shared_info_init(kvm, data->u.shared_info.gfn);
+
+		idx = srcu_read_lock(&kvm->srcu);
+
+		if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
+			kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
+			r = 0;
+		} else {
+			r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
+					     gfn_to_gpa(data->u.shared_info.gfn),
+					     PAGE_SIZE);
+		}
+
+		srcu_read_unlock(&kvm->srcu, idx);
+
+		if (!r && kvm->arch.xen.shinfo_cache.active)
+			r = kvm_xen_shared_info_init(kvm);
+
 		mutex_unlock(&kvm->arch.xen.xen_lock);
 		break;
-
+	}
 	case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
 		if (data->u.vector && data->u.vector < 0x10)
 			r = -EINVAL;
-- 
2.39.2

[PATCH v13 11/21] KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is set

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

If the shared_info PFN cache has already been initialized then the content
of the shared_info page needs to be re-initialized whenever the guest
mode is (re)set.
Setting the guest mode is either done explicitly by the VMM via the
KVM_XEN_ATTR_TYPE_LONG_MODE attribute, or implicitly when the guest writes
the MSR to set up the hypercall page.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v12:
 - Fix missing update of return value if mode is not actually changed.

v11:
 - Drop the hunk removing the call to kvm_xen_shared_info_init() when
   KVM_XEN_ATTR_TYPE_SHARED_INFO is set; it was a mistake and causes self-
   test failures.

v10:
 - New in this version.
---
 arch/x86/kvm/xen.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 031e98d88ba2..52edf676c471 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -625,8 +625,16 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		} else {
 			mutex_lock(&kvm->arch.xen.xen_lock);
 			kvm->arch.xen.long_mode = !!data->u.long_mode;
+
+			/*
+			 * Re-initialize shared_info to put the wallclock in the
+			 * correct place. Whilst it's not necessary to do this
+			 * unless the mode is actually changed, it does no harm
+			 * to make the call anyway.
+			 */
+			r = kvm->arch.xen.shinfo_cache.active ?
+				kvm_xen_shared_info_init(kvm) : 0;
 			mutex_unlock(&kvm->arch.xen.xen_lock);
-			r = 0;
 		}
 		break;
 
@@ -1101,9 +1109,24 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
 	u32 page_num = data & ~PAGE_MASK;
 	u64 page_addr = data & PAGE_MASK;
 	bool lm = is_long_mode(vcpu);
+	int r = 0;
+
+	mutex_lock(&kvm->arch.xen.xen_lock);
+	if (kvm->arch.xen.long_mode != lm) {
+		kvm->arch.xen.long_mode = lm;
+
+		/*
+		 * Re-initialize shared_info to put the wallclock in the
+		 * correct place.
+		 */
+		if (kvm->arch.xen.shinfo_cache.active &&
+		    kvm_xen_shared_info_init(kvm))
+			r = 1;
+	}
+	mutex_unlock(&kvm->arch.xen.xen_lock);
 
-	/* Latch long_mode for shared_info pages etc. */
-	vcpu->kvm->arch.xen.long_mode = lm;
+	if (r)
+		return r;
 
 	/*
 	 * If Xen hypercall intercept is enabled, fill the hypercall
-- 
2.39.2

[PATCH v13 12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

The shared_info page is not guest memory as such. It is a dedicated page
allocated by the VMM and overlaid onto guest memory in a GFN chosen by the
guest and specified in the XENMEM_add_to_physmap hypercall. The guest may
even request that shared_info be moved from one GFN to another by
re-issuing that hypercall, but the HVA is never going to change.

Because the shared_info page is an overlay the memory slots need to be
updated in response to the hypercall. However, memory slot adjustment is
not atomic and, whilst all vCPUs are paused, there is still the possibility
that events may be delivered (which requires the shared_info page to be
updated) whilst the shared_info GPA is absent. The HVA is never absent
though, so it makes much more sense to use that as the basis for the
kernel's mapping.

Hence add a new KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA attribute type for this
purpose and a KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA flag to advertize its
availability. Don't actually advertize it yet though. That will be done in
a subsequent patch, which will also add tests for the new attribute type.

Also update the KVM API documentation with the new attribute and also fix
it up to consistently refer to 'shared_info' (with the underscore).

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org

v13:
 - Patch title change.
 - Properly validate HVAs.

v8:
 - Re-base.

v2:
 - Define the new attribute and capability but don't advertize the
   capability yet.
 - Add API documentation.
---
 Documentation/virt/kvm/api.rst | 25 ++++++++++++++-----
 arch/x86/kvm/xen.c             | 44 +++++++++++++++++++++++++++-------
 include/uapi/linux/kvm.h       |  6 ++++-
 3 files changed, 59 insertions(+), 16 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 3ec0b7a455a0..3372be85b335 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -372,7 +372,7 @@ The bits in the dirty bitmap are cleared before the ioctl returns, unless
 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled.  For more information,
 see the description of the capability.
 
-Note that the Xen shared info page, if configured, shall always be assumed
+Note that the Xen shared_info page, if configured, shall always be assumed
 to be dirty. KVM will not explicitly mark it such.
 
 
@@ -5487,8 +5487,9 @@ KVM_PV_ASYNC_CLEANUP_PERFORM
 		__u8 long_mode;
 		__u8 vector;
 		__u8 runstate_update_flag;
-		struct {
+		union {
 			__u64 gfn;
+			__u64 hva;
 		} shared_info;
 		struct {
 			__u32 send_port;
@@ -5516,10 +5517,10 @@ type values:
 
 KVM_XEN_ATTR_TYPE_LONG_MODE
   Sets the ABI mode of the VM to 32-bit or 64-bit (long mode). This
-  determines the layout of the shared info pages exposed to the VM.
+  determines the layout of the shared_info page exposed to the VM.
 
 KVM_XEN_ATTR_TYPE_SHARED_INFO
-  Sets the guest physical frame number at which the Xen "shared info"
+  Sets the guest physical frame number at which the Xen shared_info
   page resides. Note that although Xen places vcpu_info for the first
   32 vCPUs in the shared_info page, KVM does not automatically do so
   and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO be used
@@ -5528,7 +5529,7 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO
   not be aware of the Xen CPU id which is used as the index into the
   vcpu_info[] array, so may know the correct default location.
 
-  Note that the shared info page may be constantly written to by KVM;
+  Note that the shared_info page may be constantly written to by KVM;
   it contains the event channel bitmap used to deliver interrupts to
   a Xen guest, amongst other things. It is exempt from dirty tracking
   mechanisms — KVM will not explicitly mark the page as dirty each
@@ -5537,9 +5538,21 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO
   any vCPU has been running or any event channel interrupts can be
   routed to the guest.
 
-  Setting the gfn to KVM_XEN_INVALID_GFN will disable the shared info
+  Setting the gfn to KVM_XEN_INVALID_GFN will disable the shared_info
   page.
 
+KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA
+  If the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA flag is also set in the
+  Xen capabilities, then this attribute may be used to set the
+  userspace address at which the shared_info page resides, which
+  will always be fixed in the VMM regardless of where it is mapped
+  in guest physical address space. This attribute should be used in
+  preference to KVM_XEN_ATTR_TYPE_SHARED_INFO as it avoids
+  unnecessary invalidation of an internal cache when the page is
+  re-mapped in guest physcial address space.
+
+  Setting the hva to zero will disable the shared_info page.
+
 KVM_XEN_ATTR_TYPE_UPCALL_VECTOR
   Sets the exception vector used to deliver Xen event channel upcalls.
   This is the HVM-wide vector injected directly by the hypervisor
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 52edf676c471..6fb268e424fa 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -617,7 +617,6 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 {
 	int r = -ENOENT;
 
-
 	switch (data->type) {
 	case KVM_XEN_ATTR_TYPE_LONG_MODE:
 		if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode) {
@@ -638,20 +637,37 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		}
 		break;
 
-	case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA: {
 		int idx;
 
 		mutex_lock(&kvm->arch.xen.xen_lock);
 
 		idx = srcu_read_lock(&kvm->srcu);
 
-		if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
-			kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
-			r = 0;
+		if (data->type == KVM_XEN_ATTR_TYPE_SHARED_INFO) {
+			gfn_t gfn = data->u.shared_info.gfn;
+
+			if (gfn == KVM_XEN_INVALID_GFN) {
+				kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
+				r = 0;
+			} else {
+				r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
+						     gfn_to_gpa(gfn), PAGE_SIZE);
+			}
 		} else {
-			r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
-					     gfn_to_gpa(data->u.shared_info.gfn),
-					     PAGE_SIZE);
+			unsigned long hva = data->u.shared_info.hva;
+
+			if (!PAGE_ALIGNED(hva) ||
+			    !access_ok((void __user *)hva, PAGE_SIZE)) {
+				r = -EINVAL;
+			} else if (!hva) {
+				kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
+				r = 0;
+			} else {
+				r = kvm_gpc_activate_hva(&kvm->arch.xen.shinfo_cache,
+							 hva, PAGE_SIZE);
+			}
 		}
 
 		srcu_read_unlock(&kvm->srcu, idx);
@@ -715,13 +731,23 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		break;
 
 	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
-		if (kvm->arch.xen.shinfo_cache.active)
+		if (kvm->arch.xen.shinfo_cache.active &&
+		    kvm->arch.xen.shinfo_cache.gpa != KVM_XEN_INVALID_GPA)
 			data->u.shared_info.gfn = gpa_to_gfn(kvm->arch.xen.shinfo_cache.gpa);
 		else
 			data->u.shared_info.gfn = KVM_XEN_INVALID_GFN;
 		r = 0;
 		break;
 
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA:
+		if (kvm->arch.xen.shinfo_cache.active &&
+		    kvm->arch.xen.shinfo_cache.gpa == KVM_XEN_INVALID_GPA)
+			data->u.shared_info.hva = kvm->arch.xen.shinfo_cache.uhva;
+		else
+			data->u.shared_info.hva = 0;
+		r = 0;
+		break;
+
 	case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
 		data->u.vector = kvm->arch.xen.upcall_vector;
 		r = 0;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index c3308536482b..ac5caba313d1 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1246,6 +1246,7 @@ struct kvm_x86_mce {
 #define KVM_XEN_HVM_CONFIG_EVTCHN_SEND		(1 << 5)
 #define KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG	(1 << 6)
 #define KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE	(1 << 7)
+#define KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA	(1 << 8)
 
 struct kvm_xen_hvm_config {
 	__u32 flags;
@@ -1744,9 +1745,10 @@ struct kvm_xen_hvm_attr {
 		__u8 long_mode;
 		__u8 vector;
 		__u8 runstate_update_flag;
-		struct {
+		union {
 			__u64 gfn;
 #define KVM_XEN_INVALID_GFN ((__u64)-1)
+			__u64 hva;
 		} shared_info;
 		struct {
 			__u32 send_port;
@@ -1788,6 +1790,8 @@ struct kvm_xen_hvm_attr {
 #define KVM_XEN_ATTR_TYPE_XEN_VERSION		0x4
 /* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG */
 #define KVM_XEN_ATTR_TYPE_RUNSTATE_UPDATE_FLAG	0x5
+/* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA */
+#define KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA	0x6
 
 /* Per-vCPU Xen attributes */
 #define KVM_XEN_VCPU_GET_ATTR	_IOWR(KVMIO, 0xca, struct kvm_xen_vcpu_attr)
-- 
2.39.2

Re: [PATCH v13 12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> @@ -715,13 +731,23 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
>  		break;
>  
>  	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
> -		if (kvm->arch.xen.shinfo_cache.active)
> +		if (kvm->arch.xen.shinfo_cache.active &&
> +		    kvm->arch.xen.shinfo_cache.gpa != KVM_XEN_INVALID_GPA)

This should really use INVALID_GPA when checking internal gpc state.  Mostly to
help clarify what is/isn't KVM Xen ABI, but also because I don't like the subtle
assumption that KVM_XEN_INVALID_GPA == INVALID_GPA.

Even better, if we slot in two helpers when the HVA-based GPC support is added,
then the Xen code doesn't need to to make assumptions about how the GPC code
manages HVA vs. GPA internally.  E.g. if we ever refactor the code again and use
a dedicated flag instead of gpc->gpa as the implicit flag.

  static inline bool kvm_gpc_is_gpa_active(struct gfn_to_pfn_cache *gpc)
  {
	return gpc->active && !kvm_is_error_gpa(gpc->gpa);
  }

  static inline bool kvm_gpc_is_hva_active(struct gfn_to_pfn_cache *gpc)
  {
	return gpc->active && kvm_is_error_gpa(gpc->gpa);
  }

Re: [PATCH v13 12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA

[Paul Durrant]

On 19/02/2024 21:53, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> @@ -715,13 +731,23 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
>>   		break;
>>   
>>   	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
>> -		if (kvm->arch.xen.shinfo_cache.active)
>> +		if (kvm->arch.xen.shinfo_cache.active &&
>> +		    kvm->arch.xen.shinfo_cache.gpa != KVM_XEN_INVALID_GPA)
> 
> This should really use INVALID_GPA when checking internal gpc state.  Mostly to
> help clarify what is/isn't KVM Xen ABI, but also because I don't like the subtle
> assumption that KVM_XEN_INVALID_GPA == INVALID_GPA.
> 

Sorry, yes, that was miss on my part.

> Even better, if we slot in two helpers when the HVA-based GPC support is added,
> then the Xen code doesn't need to to make assumptions about how the GPC code
> manages HVA vs. GPA internally.  E.g. if we ever refactor the code again and use
> a dedicated flag instead of gpc->gpa as the implicit flag.
> 
>    static inline bool kvm_gpc_is_gpa_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && !kvm_is_error_gpa(gpc->gpa);
>    }
> 
>    static inline bool kvm_gpc_is_hva_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && kvm_is_error_gpa(gpc->gpa);
>    }

Sure, sounds good to me. I'll add those.

[PATCH v13 13/21] KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

If the guest does not explicitly set the GPA of vcpu_info structure in
memory then, for guests with 32 vCPUs or fewer, the vcpu_info embedded
in the shared_info page may be used. As described in a previous commit,
the shared_info page is an overlay at a fixed HVA within the VMM, so in
this case it also more optimal to activate the vcpu_info cache with a
fixed HVA to avoid unnecessary invalidation if the guest memory layout
is modified.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org

v13:
 - Patch title change.

v8:
 - Re-base.

v5:
 - New in this version.
---
 Documentation/virt/kvm/api.rst | 26 +++++++++++++++++++++-----
 arch/x86/kvm/xen.c             | 34 ++++++++++++++++++++++++++++------
 include/uapi/linux/kvm.h       |  3 +++
 3 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 3372be85b335..bd93cafd3e4e 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5523,11 +5523,12 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO
   Sets the guest physical frame number at which the Xen shared_info
   page resides. Note that although Xen places vcpu_info for the first
   32 vCPUs in the shared_info page, KVM does not automatically do so
-  and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO be used
-  explicitly even when the vcpu_info for a given vCPU resides at the
-  "default" location in the shared_info page. This is because KVM may
-  not be aware of the Xen CPU id which is used as the index into the
-  vcpu_info[] array, so may know the correct default location.
+  and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO or
+  KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA be used explicitly even when
+  the vcpu_info for a given vCPU resides at the "default" location
+  in the shared_info page. This is because KVM may not be aware of
+  the Xen CPU id which is used as the index into the vcpu_info[]
+  array, so may know the correct default location.
 
   Note that the shared_info page may be constantly written to by KVM;
   it contains the event channel bitmap used to deliver interrupts to
@@ -5649,6 +5650,21 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO
   on dirty logging. Setting the gpa to KVM_XEN_INVALID_GPA will disable
   the vcpu_info.
 
+KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA
+  If the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA flag is also set in the
+  Xen capabilities, then this attribute may be used to set the
+  userspace address of the vcpu_info for a given vCPU. It should
+  only be used when the vcpu_info resides at the "default" location
+  in the shared_info page. In this case it is safe to assume the
+  userspace address will not change, because the shared_info page is
+  an overlay on guest memory and remains at a fixed host address
+  regardless of where it is mapped in guest physical address space
+  and hence unnecessary invalidation of an internal cache may be
+  avoided if the guest memory layout is modified.
+  If the vcpu_info does not reside at the "default" location then
+  it is not guaranteed to remain at the same host address and
+  hence the aforementioned cache invalidation is required.
+
 KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO
   Sets the guest physical address of an additional pvclock structure
   for a given vCPU. This is typically used for guest vsyscall support.
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 6fb268e424fa..4e79cc68e0a9 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -784,20 +784,33 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 
 	switch (data->type) {
 	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO:
+	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA:
 		/* No compat necessary here. */
 		BUILD_BUG_ON(sizeof(struct vcpu_info) !=
 			     sizeof(struct compat_vcpu_info));
 		BUILD_BUG_ON(offsetof(struct vcpu_info, time) !=
 			     offsetof(struct compat_vcpu_info, time));
 
-		if (data->u.gpa == KVM_XEN_INVALID_GPA) {
-			kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
-			r = 0;
-			break;
+		if (data->type == KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO) {
+			if (data->u.gpa == KVM_XEN_INVALID_GPA) {
+				kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
+				r = 0;
+				break;
+			}
+
+			r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache,
+					     data->u.gpa, sizeof(struct vcpu_info));
+		} else {
+			if (data->u.hva == 0) {
+				kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
+				r = 0;
+				break;
+			}
+
+			r = kvm_gpc_activate_hva(&vcpu->arch.xen.vcpu_info_cache,
+						 data->u.hva, sizeof(struct vcpu_info));
 		}
 
-		r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache,
-				     data->u.gpa, sizeof(struct vcpu_info));
 		if (!r)
 			kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 
@@ -1026,6 +1039,15 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		r = 0;
 		break;
 
+	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA:
+		if (vcpu->arch.xen.vcpu_info_cache.active &&
+		    vcpu->arch.xen.vcpu_info_cache.gpa == KVM_XEN_INVALID_GPA)
+			data->u.hva = vcpu->arch.xen.vcpu_info_cache.uhva;
+		else
+			data->u.hva = 0;
+		r = 0;
+		break;
+
 	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO:
 		if (vcpu->arch.xen.vcpu_time_info_cache.active)
 			data->u.gpa = vcpu->arch.xen.vcpu_time_info_cache.gpa;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index ac5caba313d1..d2665319db6e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1809,6 +1809,7 @@ struct kvm_xen_vcpu_attr {
 	union {
 		__u64 gpa;
 #define KVM_XEN_INVALID_GPA ((__u64)-1)
+		__u64 hva;
 		__u64 pad[8];
 		struct {
 			__u64 state;
@@ -1839,6 +1840,8 @@ struct kvm_xen_vcpu_attr {
 #define KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID		0x6
 #define KVM_XEN_VCPU_ATTR_TYPE_TIMER		0x7
 #define KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR	0x8
+/* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA */
+#define KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA	0x9
 
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
-- 
2.39.2

[PATCH v13 14/21] KVM: selftests: map Xen's shared_info page using HVA rather than GFN

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Using the HVA of the shared_info page is more efficient, so if the
capability (KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA) is present use that method
to do the mapping.

NOTE: Have the juggle_shinfo_state() thread map and unmap using both
      GFN and HVA, to make sure the older mechanism is not broken.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v13:
 - Patch title change.

v3:
 - Re-work the juggle_shinfo_state() thread.

v2:
 - New in this version.
---
 .../selftests/kvm/x86_64/xen_shinfo_test.c    | 44 +++++++++++++++----
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
index 9ec9ab60b63e..a61500ff0822 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
@@ -389,6 +389,7 @@ static int cmp_timespec(struct timespec *a, struct timespec *b)
 		return 0;
 }
 
+static struct shared_info *shinfo;
 static struct vcpu_info *vinfo;
 static struct kvm_vcpu *vcpu;
 
@@ -404,20 +405,38 @@ static void *juggle_shinfo_state(void *arg)
 {
 	struct kvm_vm *vm = (struct kvm_vm *)arg;
 
-	struct kvm_xen_hvm_attr cache_activate = {
+	struct kvm_xen_hvm_attr cache_activate_gfn = {
 		.type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
 		.u.shared_info.gfn = SHINFO_REGION_GPA / PAGE_SIZE
 	};
 
-	struct kvm_xen_hvm_attr cache_deactivate = {
+	struct kvm_xen_hvm_attr cache_deactivate_gfn = {
 		.type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
 		.u.shared_info.gfn = KVM_XEN_INVALID_GFN
 	};
 
+	struct kvm_xen_hvm_attr cache_activate_hva = {
+		.type = KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA,
+		.u.shared_info.hva = (unsigned long)shinfo
+	};
+
+	struct kvm_xen_hvm_attr cache_deactivate_hva = {
+		.type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
+		.u.shared_info.hva = 0
+	};
+
+	int xen_caps = kvm_check_cap(KVM_CAP_XEN_HVM);
+
 	for (;;) {
-		__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_activate);
-		__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_deactivate);
+		__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_activate_gfn);
 		pthread_testcancel();
+		__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_deactivate_gfn);
+
+		if (xen_caps & KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA) {
+			__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_activate_hva);
+			pthread_testcancel();
+			__vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_deactivate_hva);
+		}
 	}
 
 	return NULL;
@@ -442,6 +461,7 @@ int main(int argc, char *argv[])
 	bool do_runstate_flag = !!(xen_caps & KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG);
 	bool do_eventfd_tests = !!(xen_caps & KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL);
 	bool do_evtchn_tests = do_eventfd_tests && !!(xen_caps & KVM_XEN_HVM_CONFIG_EVTCHN_SEND);
+	bool has_shinfo_hva = !!(xen_caps & KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA);
 
 	clock_gettime(CLOCK_REALTIME, &min_ts);
 
@@ -452,7 +472,7 @@ int main(int argc, char *argv[])
 				    SHINFO_REGION_GPA, SHINFO_REGION_SLOT, 3, 0);
 	virt_map(vm, SHINFO_REGION_GVA, SHINFO_REGION_GPA, 3);
 
-	struct shared_info *shinfo = addr_gpa2hva(vm, SHINFO_VADDR);
+	shinfo = addr_gpa2hva(vm, SHINFO_VADDR);
 
 	int zero_fd = open("/dev/zero", O_RDONLY);
 	TEST_ASSERT(zero_fd != -1, "Failed to open /dev/zero");
@@ -488,10 +508,16 @@ int main(int argc, char *argv[])
 			    "Failed to read back RUNSTATE_UPDATE_FLAG attr");
 	}
 
-	struct kvm_xen_hvm_attr ha = {
-		.type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
-		.u.shared_info.gfn = SHINFO_REGION_GPA / PAGE_SIZE,
-	};
+	struct kvm_xen_hvm_attr ha = {};
+
+	if (has_shinfo_hva) {
+		ha.type = KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA;
+		ha.u.shared_info.hva = (unsigned long)shinfo;
+	} else {
+		ha.type = KVM_XEN_ATTR_TYPE_SHARED_INFO;
+		ha.u.shared_info.gfn = SHINFO_ADDR / PAGE_SIZE;
+	}
+
 	vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &ha);
 
 	/*
-- 
2.39.2

[PATCH v13 15/21] KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

If the relevant capability (KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA) is present
then re-map vcpu_info using the HVA part way through the tests to make sure
then there is no functional change.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v13:
 - Patch title change.

v5:
 - New in this version.
---
 .../selftests/kvm/x86_64/xen_shinfo_test.c        | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
index a61500ff0822..d2ea0435f4f7 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
@@ -62,6 +62,7 @@ enum {
 	TEST_POLL_TIMEOUT,
 	TEST_POLL_MASKED,
 	TEST_POLL_WAKE,
+	SET_VCPU_INFO,
 	TEST_TIMER_PAST,
 	TEST_LOCKING_SEND_RACE,
 	TEST_LOCKING_POLL_RACE,
@@ -321,6 +322,10 @@ static void guest_code(void)
 
 	GUEST_SYNC(TEST_POLL_WAKE);
 
+	/* Set the vcpu_info to point at exactly the place it already is to
+	 * make sure the attribute is functional. */
+	GUEST_SYNC(SET_VCPU_INFO);
+
 	/* A timer wake an *unmasked* port which should wake us with an
 	 * actual interrupt, while we're polling on a different port. */
 	ports[0]++;
@@ -888,6 +893,16 @@ int main(int argc, char *argv[])
 				alarm(1);
 				break;
 
+			case SET_VCPU_INFO:
+				if (has_shinfo_hva) {
+					struct kvm_xen_vcpu_attr vih = {
+						.type = KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA,
+						.u.hva = (unsigned long)vinfo
+					};
+					vcpu_ioctl(vcpu, KVM_XEN_VCPU_SET_ATTR, &vih);
+				}
+				break;
+
 			case TEST_TIMER_PAST:
 				TEST_ASSERT(!evtchn_irq_expected,
 					    "Expected event channel IRQ but it didn't happen");
-- 
2.39.2

[PATCH v13 16/21] KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

Now that all relevant kernel changes and selftests are in place, enable the
new capability.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v2:
 - New in this version.
---
 arch/x86/kvm/x86.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 31cd5d803dae..9f98c5075629 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4673,7 +4673,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		    KVM_XEN_HVM_CONFIG_SHARED_INFO |
 		    KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL |
 		    KVM_XEN_HVM_CONFIG_EVTCHN_SEND |
-		    KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE;
+		    KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE |
+		    KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA;
 		if (sched_info_on())
 			r |= KVM_XEN_HVM_CONFIG_RUNSTATE |
 			     KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG;
-- 
2.39.2

[PATCH v13 17/21] KVM: x86/xen: split up kvm_xen_set_evtchn_fast()

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

The implementation of kvm_xen_set_evtchn_fast() is a rather lengthy piece
of code that performs two operations: updating of the shared_info
evtchn_pending mask, and updating of the vcpu_info evtchn_pending_sel
mask. Introduce a separate function to perform each of those operations and
re-work kvm_xen_set_evtchn_fast() to use them.

No functional change intended.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v11:
 - Fixed /64 vs /32 switcheroo and changed type of port_word_bit back to
   int.

v10:
 - Updated in this version. Dropped David'd R-b since the updates are
   non-trivial.

v8:
 - New in this version.
---
 arch/x86/kvm/xen.c | 175 ++++++++++++++++++++++++++-------------------
 1 file changed, 100 insertions(+), 75 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 4e79cc68e0a9..59073642c078 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1670,6 +1670,101 @@ static void kvm_xen_check_poller(struct kvm_vcpu *vcpu, int port)
 	}
 }
 
+static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
+{
+	struct kvm *kvm = vcpu->kvm;
+	struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
+	unsigned long *pending_bits, *mask_bits;
+	unsigned long flags;
+	int rc = -EWOULDBLOCK;
+
+	read_lock_irqsave(&gpc->lock, flags);
+	if (!kvm_gpc_check(gpc, PAGE_SIZE))
+		goto out;
+
+	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+		struct shared_info *shinfo = gpc->khva;
+
+		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
+		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
+	} else {
+		struct compat_shared_info *shinfo = gpc->khva;
+
+		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
+		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
+	}
+
+	if (test_and_set_bit(port, pending_bits)) {
+		rc = 0; /* It was already raised */
+	} else if (test_bit(port, mask_bits)) {
+		rc = -ENOTCONN; /* It is masked */
+		kvm_xen_check_poller(vcpu, port);
+	} else {
+		rc = 1; /* It is newly raised */
+	}
+
+ out:
+	read_unlock_irqrestore(&gpc->lock, flags);
+	return rc;
+}
+
+static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
+{
+	struct kvm *kvm = vcpu->kvm;
+	struct gfn_to_pfn_cache *gpc = &vcpu->arch.xen.vcpu_info_cache;
+	unsigned long flags;
+	bool kick_vcpu = false;
+
+	read_lock_irqsave(&gpc->lock, flags);
+
+	/*
+	 * Try to deliver the event directly to the vcpu_info. If successful and
+	 * the guest is using upcall_vector delivery, send the MSI.
+	 * If the pfncache is invalid, set the shadow. In this case, or if the
+	 * guest is using another form of event delivery, the vCPU must be
+	 * kicked to complete the delivery.
+	 */
+	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
+		struct vcpu_info *vcpu_info = gpc->khva;
+		int port_word_bit = port / 64;
+
+		if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) {
+			if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
+				kick_vcpu = true;
+			goto out;
+		}
+
+		if (!test_and_set_bit(port_word_bit, &vcpu_info->evtchn_pending_sel)) {
+			WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
+			kick_vcpu = true;
+		}
+	} else {
+		struct compat_vcpu_info *vcpu_info = gpc->khva;
+		int port_word_bit = port / 32;
+
+		if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) {
+			if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
+				kick_vcpu = true;
+			goto out;
+		}
+
+		if (!test_and_set_bit(port_word_bit,
+				      (unsigned long *)&vcpu_info->evtchn_pending_sel)) {
+			WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
+			kick_vcpu = true;
+		}
+	}
+
+	if (kick_vcpu && vcpu->arch.xen.upcall_vector) {
+		kvm_xen_inject_vcpu_vector(vcpu);
+		kick_vcpu = false;
+	}
+
+ out:
+	read_unlock_irqrestore(&gpc->lock, flags);
+	return kick_vcpu;
+}
+
 /*
  * The return value from this function is propagated to kvm_set_irq() API,
  * so it returns:
@@ -1678,15 +1773,12 @@ static void kvm_xen_check_poller(struct kvm_vcpu *vcpu, int port)
  *  > 0   Number of CPUs interrupt was delivered to
  *
  * It is also called directly from kvm_arch_set_irq_inatomic(), where the
- * only check on its return value is a comparison with -EWOULDBLOCK'.
+ * only check on its return value is a comparison with -EWOULDBLOCK
+ * (which may be returned by set_shinfo_evtchn_pending()).
  */
 int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 {
-	struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
 	struct kvm_vcpu *vcpu;
-	unsigned long *pending_bits, *mask_bits;
-	unsigned long flags;
-	int port_word_bit;
 	bool kick_vcpu = false;
 	int vcpu_idx, idx, rc;
 
@@ -1706,79 +1798,12 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 	if (xe->port >= max_evtchn_port(kvm))
 		return -EINVAL;
 
-	rc = -EWOULDBLOCK;
-
 	idx = srcu_read_lock(&kvm->srcu);
 
-	read_lock_irqsave(&gpc->lock, flags);
-	if (!kvm_gpc_check(gpc, PAGE_SIZE))
-		goto out_rcu;
-
-	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
-		struct shared_info *shinfo = gpc->khva;
-		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
-		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
-		port_word_bit = xe->port / 64;
-	} else {
-		struct compat_shared_info *shinfo = gpc->khva;
-		pending_bits = (unsigned long *)&shinfo->evtchn_pending;
-		mask_bits = (unsigned long *)&shinfo->evtchn_mask;
-		port_word_bit = xe->port / 32;
-	}
+	rc = set_shinfo_evtchn_pending(vcpu, xe->port);
+	if (rc == 1) /* Delivered to the bitmap in shared_info */
+		kick_vcpu = set_vcpu_info_evtchn_pending(vcpu, xe->port);
 
-	/*
-	 * If this port wasn't already set, and if it isn't masked, then
-	 * we try to set the corresponding bit in the in-kernel shadow of
-	 * evtchn_pending_sel for the target vCPU. And if *that* wasn't
-	 * already set, then we kick the vCPU in question to write to the
-	 * *real* evtchn_pending_sel in its own guest vcpu_info struct.
-	 */
-	if (test_and_set_bit(xe->port, pending_bits)) {
-		rc = 0; /* It was already raised */
-	} else if (test_bit(xe->port, mask_bits)) {
-		rc = -ENOTCONN; /* Masked */
-		kvm_xen_check_poller(vcpu, xe->port);
-	} else {
-		rc = 1; /* Delivered to the bitmap in shared_info. */
-		/* Now switch to the vCPU's vcpu_info to set the index and pending_sel */
-		read_unlock_irqrestore(&gpc->lock, flags);
-		gpc = &vcpu->arch.xen.vcpu_info_cache;
-
-		read_lock_irqsave(&gpc->lock, flags);
-		if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
-			/*
-			 * Could not access the vcpu_info. Set the bit in-kernel
-			 * and prod the vCPU to deliver it for itself.
-			 */
-			if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
-				kick_vcpu = true;
-			goto out_rcu;
-		}
-
-		if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
-			struct vcpu_info *vcpu_info = gpc->khva;
-			if (!test_and_set_bit(port_word_bit, &vcpu_info->evtchn_pending_sel)) {
-				WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
-				kick_vcpu = true;
-			}
-		} else {
-			struct compat_vcpu_info *vcpu_info = gpc->khva;
-			if (!test_and_set_bit(port_word_bit,
-					      (unsigned long *)&vcpu_info->evtchn_pending_sel)) {
-				WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
-				kick_vcpu = true;
-			}
-		}
-
-		/* For the per-vCPU lapic vector, deliver it as MSI. */
-		if (kick_vcpu && vcpu->arch.xen.upcall_vector) {
-			kvm_xen_inject_vcpu_vector(vcpu);
-			kick_vcpu = false;
-		}
-	}
-
- out_rcu:
-	read_unlock_irqrestore(&gpc->lock, flags);
 	srcu_read_unlock(&kvm->srcu, idx);
 
 	if (kick_vcpu) {
-- 
2.39.2

[PATCH v13 18/21] KVM: x86/xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

As described in [1] compiling with CONFIG_PROVE_RAW_LOCK_NESTING shows that
kvm_xen_set_evtchn_fast() is blocking on pfncache locks in IRQ context.
There is only actually blocking with PREEMPT_RT because the locks will
turned into mutexes. There is no 'raw' version of rwlock_t that can be used
to avoid that, so use read_trylock() and treat failure to lock the same as
an invalid cache.

[1] https://lore.kernel.org/lkml/99771ef3a4966a01fefd3adbb2ba9c3a75f97cf2.camel@infradead.org/T/#mbd06e5a04534ce9c0ee94bd8f1e8d942b2d45bd6

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v13:
 - Patch title change.

v11:
 - Amended the commit comment.

v10:
 - New in this version.
---
 arch/x86/kvm/xen.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 59073642c078..8650141b266e 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1678,10 +1678,13 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
 	unsigned long flags;
 	int rc = -EWOULDBLOCK;
 
-	read_lock_irqsave(&gpc->lock, flags);
-	if (!kvm_gpc_check(gpc, PAGE_SIZE))
+	local_irq_save(flags);
+	if (!read_trylock(&gpc->lock))
 		goto out;
 
+	if (!kvm_gpc_check(gpc, PAGE_SIZE))
+		goto out_unlock;
+
 	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
 		struct shared_info *shinfo = gpc->khva;
 
@@ -1703,8 +1706,10 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
 		rc = 1; /* It is newly raised */
 	}
 
+ out_unlock:
+	read_unlock(&gpc->lock);
  out:
-	read_unlock_irqrestore(&gpc->lock, flags);
+	local_irq_restore(flags);
 	return rc;
 }
 
@@ -1714,21 +1719,23 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
 	struct gfn_to_pfn_cache *gpc = &vcpu->arch.xen.vcpu_info_cache;
 	unsigned long flags;
 	bool kick_vcpu = false;
+	bool locked;
 
-	read_lock_irqsave(&gpc->lock, flags);
+	local_irq_save(flags);
+	locked = read_trylock(&gpc->lock);
 
 	/*
 	 * Try to deliver the event directly to the vcpu_info. If successful and
 	 * the guest is using upcall_vector delivery, send the MSI.
-	 * If the pfncache is invalid, set the shadow. In this case, or if the
-	 * guest is using another form of event delivery, the vCPU must be
-	 * kicked to complete the delivery.
+	 * If the pfncache lock is contended or the cache is invalid, set the
+	 * shadow. In this case, or if the guest is using another form of event
+	 * delivery, the vCPU must be kicked to complete the delivery.
 	 */
 	if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
 		struct vcpu_info *vcpu_info = gpc->khva;
 		int port_word_bit = port / 64;
 
-		if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) {
+		if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) {
 			if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
 				kick_vcpu = true;
 			goto out;
@@ -1742,7 +1749,7 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
 		struct compat_vcpu_info *vcpu_info = gpc->khva;
 		int port_word_bit = port / 32;
 
-		if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) {
+		if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) {
 			if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel))
 				kick_vcpu = true;
 			goto out;
@@ -1761,7 +1768,10 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
 	}
 
  out:
-	read_unlock_irqrestore(&gpc->lock, flags);
+	if (locked)
+		read_unlock(&gpc->lock);
+
+	local_irq_restore(flags);
 	return kick_vcpu;
 }
 
-- 
2.39.2

Re: [PATCH v13 18/21] KVM: x86/xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@amazon.com>
> 
> As described in [1] compiling with CONFIG_PROVE_RAW_LOCK_NESTING shows that
> kvm_xen_set_evtchn_fast() is blocking on pfncache locks in IRQ context.
> There is only actually blocking with PREEMPT_RT because the locks will
> turned into mutexes. There is no 'raw' version of rwlock_t that can be used
> to avoid that, so use read_trylock() and treat failure to lock the same as
> an invalid cache.
> 
> [1] https://lore.kernel.org/lkml/99771ef3a4966a01fefd3adbb2ba9c3a75f97cf2.camel@infradead.org/T/#mbd06e5a04534ce9c0ee94bd8f1e8d942b2d45bd6
> 
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: x86@kernel.org
> 
> v13:
>  - Patch title change.
> 
> v11:
>  - Amended the commit comment.
> 
> v10:
>  - New in this version.
> ---
>  arch/x86/kvm/xen.c | 30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 59073642c078..8650141b266e 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -1678,10 +1678,13 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
>  	unsigned long flags;
>  	int rc = -EWOULDBLOCK;
>  
> -	read_lock_irqsave(&gpc->lock, flags);
> -	if (!kvm_gpc_check(gpc, PAGE_SIZE))
> +	local_irq_save(flags);
> +	if (!read_trylock(&gpc->lock))
>  		goto out;

I am not comfortable applying this patch.  As shown by the need for the next patch
to optimize unrelated invalidations, switching to read_trylock() is more subtle
than it seems at first glance.  Specifically, there are no fairness guarantees.

I am not dead set against this change, but I don't want to put my SoB on what I
consider to be a hack.

I've zero objections if you can convince Paolo to take this directly, i.e. this
isn't a NAK.  I just don't want to take it through my tree.

Re: [PATCH v13 18/21] KVM: x86/xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()

[Paul Durrant]

On 19/02/2024 22:04, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> From: Paul Durrant <pdurrant@amazon.com>
>>
>> As described in [1] compiling with CONFIG_PROVE_RAW_LOCK_NESTING shows that
>> kvm_xen_set_evtchn_fast() is blocking on pfncache locks in IRQ context.
>> There is only actually blocking with PREEMPT_RT because the locks will
>> turned into mutexes. There is no 'raw' version of rwlock_t that can be used
>> to avoid that, so use read_trylock() and treat failure to lock the same as
>> an invalid cache.
>>
>> [1] https://lore.kernel.org/lkml/99771ef3a4966a01fefd3adbb2ba9c3a75f97cf2.camel@infradead.org/T/#mbd06e5a04534ce9c0ee94bd8f1e8d942b2d45bd6
>>
>> Signed-off-by: Paul Durrant <pdurrant@amazon.com>
>> Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
>> ---
>> Cc: Sean Christopherson <seanjc@google.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: David Woodhouse <dwmw2@infradead.org>
>> Cc: x86@kernel.org
>>
>> v13:
>>   - Patch title change.
>>
>> v11:
>>   - Amended the commit comment.
>>
>> v10:
>>   - New in this version.
>> ---
>>   arch/x86/kvm/xen.c | 30 ++++++++++++++++++++----------
>>   1 file changed, 20 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
>> index 59073642c078..8650141b266e 100644
>> --- a/arch/x86/kvm/xen.c
>> +++ b/arch/x86/kvm/xen.c
>> @@ -1678,10 +1678,13 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
>>   	unsigned long flags;
>>   	int rc = -EWOULDBLOCK;
>>   
>> -	read_lock_irqsave(&gpc->lock, flags);
>> -	if (!kvm_gpc_check(gpc, PAGE_SIZE))
>> +	local_irq_save(flags);
>> +	if (!read_trylock(&gpc->lock))
>>   		goto out;
> 
> I am not comfortable applying this patch.  As shown by the need for the next patch
> to optimize unrelated invalidations, switching to read_trylock() is more subtle
> than it seems at first glance.  Specifically, there are no fairness guarantees.
> 
> I am not dead set against this change, but I don't want to put my SoB on what I
> consider to be a hack.
> 
> I've zero objections if you can convince Paolo to take this directly, i.e. this
> isn't a NAK.  I just don't want to take it through my tree.

Ok. I'll drop this from v14 then. It can go separately, assuming there 
is no move to add the raw lock which would negate it.

[PATCH v13 19/21] KVM: pfncache: check the need for invalidation under read lock first

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

When processing mmu_notifier invalidations for gpc caches, pre-check for
overlap with the invalidation event while holding gpc->lock for read, and
only take gpc->lock for write if the cache needs to be invalidated.  Doing
a pre-check without taking gpc->lock for write avoids unnecessarily
contending the lock for unrelated invalidations, which is very beneficial
for caches that are heavily used (but rarely subjected to mmu_notifier
invalidations).

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v13:
 - Use Sean's preferred wording for the commit comment.

v10:
 - New in this version.
---
 virt/kvm/pfncache.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 4e64d349b2f7..a60d8f906896 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -29,14 +29,30 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
 
 	spin_lock(&kvm->gpc_lock);
 	list_for_each_entry(gpc, &kvm->gpc_list, list) {
-		write_lock_irq(&gpc->lock);
+		read_lock_irq(&gpc->lock);
 
 		/* Only a single page so no need to care about length */
 		if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
 		    gpc->uhva >= start && gpc->uhva < end) {
-			gpc->valid = false;
+			read_unlock_irq(&gpc->lock);
+
+			/*
+			 * There is a small window here where the cache could
+			 * be modified, and invalidation would no longer be
+			 * necessary. Hence check again whether invalidation
+			 * is still necessary once the write lock has been
+			 * acquired.
+			 */
+
+			write_lock_irq(&gpc->lock);
+			if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
+			    gpc->uhva >= start && gpc->uhva < end)
+				gpc->valid = false;
+			write_unlock_irq(&gpc->lock);
+			continue;
 		}
-		write_unlock_irq(&gpc->lock);
+
+		read_unlock_irq(&gpc->lock);
 	}
 	spin_unlock(&kvm->gpc_lock);
 }
-- 
2.39.2

[PATCH v13 20/21] KVM: x86/xen: allow vcpu_info content to be 'safely' copied

[Paul Durrant]

From: Paul Durrant <pdurrant@amazon.com>

If the guest sets an explicit vcpu_info GPA then, for any of the first 32
vCPUs, the content of the default vcpu_info in the shared_info page must be
copied into the new location. Because this copy may race with event
delivery (which updates the 'evtchn_pending_sel' field in vcpu_info) there
needs to be a way to defer that until the copy is complete.
Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_xen
that is used in atomic context if the vcpu_info PFN cache has been
invalidated so that the update of vcpu_info can be deferred until the
cache can be refreshed (on vCPU thread's the way back into guest context).

Also use this shadow if the vcpu_info cache has been *deactivated*, so that
the VMM can safely copy the vcpu_info content and then re-activate the
cache with the new GPA. To do this, stop considering an inactive vcpu_info
cache as a hard error in kvm_xen_set_evtchn_fast().

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org

v13:
 - Patch title change.

v8:
 - Update commit comment.

v6:
 - New in this version.
---
 arch/x86/kvm/xen.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 8650141b266e..11ab62ca011d 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1802,9 +1802,6 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
 		WRITE_ONCE(xe->vcpu_idx, vcpu->vcpu_idx);
 	}
 
-	if (!vcpu->arch.xen.vcpu_info_cache.active)
-		return -EINVAL;
-
 	if (xe->port >= max_evtchn_port(kvm))
 		return -EINVAL;
 
-- 
2.39.2

[PATCH v13 21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

[Paul Durrant]

From: David Woodhouse <dwmw@amazon.co.uk>

This function can race with kvm_gpc_deactivate(), which does not take
the ->refresh_lock. This means kvm_gpc_deactivate() can wipe the ->pfn
and ->khva fields, and unmap the latter, while hva_to_pfn_retry() has
temporarily dropped its write lock on gpc->lock.

Then if hva_to_pfn_retry() determines that the PFN hasn't changed and
that the original pfn and khva can be reused, they get assigned back to
gpc->pfn and gpc->khva even though the khva was already unmapped by
kvm_gpc_deactivate(). This leaves the cache in an apparently valid state
but with ->khva pointing to an address which has been unmapped. Which in
turn leads to oopses in e.g. __kvm_xen_has_interrupt() and
set_shinfo_evtchn_pending() when they dereference said khva.

It may be possible to fix this just by making kvm_gpc_deactivate() take
the ->refresh_lock, but that still leaves ->refresh_lock being basically
redundant with the write lock on ->lock, which frankly makes my skin
itch, with the way that pfn_to_hva_retry() operates on fields in the gpc
without holding a write lock on ->lock.

Instead, fix it by cleaning up the semantics of hva_to_pfn_retry(). It
now no longer does locking gymnastics because it no longer operates on
the gpc object at all. I's called with a uhva and simply returns the
corresponding pfn (pinned), and a mapped khva for it.

Its caller __kvm_gpc_refresh() now sets gpc->uhva and clears gpc->valid
before dropping ->lock, calling hva_to_pfn_retry() and retaking ->lock
for write.

If hva_to_pfn_retry() fails, *or* if the ->uhva or ->active fields in
the gpc changed while the lock was dropped, the new mapping is discarded
and the gpc is not modified. On success with an unchanged gpc, the new
mapping is installed and the current ->pfn and ->uhva are taken into the
local old_pfn and old_khva variables to be unmapped once the locks are
all released.

This simplification means that ->refresh_lock is no longer needed for
correctness, but it does still provide a minor optimisation because it
will prevent two concurrent __kvm_gpc_refresh() calls from mapping a
given PFN, only for one of them to lose the race and discard its
mapping.

The optimisation in hva_to_pfn_retry() where it attempts to use the old
mapping if the pfn doesn't change is dropped, since it makes the pinning
more complex. It's a pointless optimisation anyway, since the odds of
the pfn ending up the same when the uhva has changed (i.e. the odds of
the two userspace addresses both pointing to the same underlying
physical page) are negligible,

The 'hva_changed' local variable in __kvm_gpc_refresh() is also removed,
since it's simpler just to clear gpc->valid if the uhva changed.
Likewise the unmap_old variable is dropped because it's just as easy to
check the old_pfn variable for KVM_PFN_ERR_FAULT.

I remain slightly confused because although this is clearly a race in
the gfn_to_pfn_cache code, I don't quite know how the Xen support code
actually managed to trigger it. We've seen oopses from dereferencing a
valid-looking ->khva in both __kvm_xen_has_interrupt() (the vcpu_info)
and in set_shinfo_evtchn_pending() (the shared_info). But surely the
race shouldn't happen for the vcpu_info gpc because all calls to both
refresh and deactivate hold the vcpu mutex, and it shouldn't happen
for the shared_info gpc because all calls to both will hold the
kvm->arch.xen.xen_lock mutex.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>

v12:
 - New in this version.
---
 virt/kvm/pfncache.c | 184 +++++++++++++++++++++-----------------------
 1 file changed, 88 insertions(+), 96 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index a60d8f906896..d1c73b452570 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -139,108 +139,65 @@ static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_s
 	return kvm->mmu_invalidate_seq != mmu_seq;
 }
 
-static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
+/*
+ * Given a user virtual address, obtain a pinned host PFN and kernel mapping
+ * for it. The caller will release the PFN after installing it into the GPC
+ * so that the MMU notifier invalidation mechanism is active.
+ */
+static kvm_pfn_t hva_to_pfn_retry(struct kvm *kvm, unsigned long uhva,
+				  kvm_pfn_t *pfn, void **khva)
 {
 	/* Note, the new page offset may be different than the old! */
-	void *old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
 	void *new_khva = NULL;
 	unsigned long mmu_seq;
 
-	lockdep_assert_held(&gpc->refresh_lock);
-
-	lockdep_assert_held_write(&gpc->lock);
-
-	/*
-	 * Invalidate the cache prior to dropping gpc->lock, the gpa=>uhva
-	 * assets have already been updated and so a concurrent check() from a
-	 * different task may not fail the gpa/uhva/generation checks.
-	 */
-	gpc->valid = false;
-
-	do {
-		mmu_seq = gpc->kvm->mmu_invalidate_seq;
+	for (;;) {
+		mmu_seq = kvm->mmu_invalidate_seq;
 		smp_rmb();
 
-		write_unlock_irq(&gpc->lock);
-
-		/*
-		 * If the previous iteration "failed" due to an mmu_notifier
-		 * event, release the pfn and unmap the kernel virtual address
-		 * from the previous attempt.  Unmapping might sleep, so this
-		 * needs to be done after dropping the lock.  Opportunistically
-		 * check for resched while the lock isn't held.
-		 */
-		if (new_pfn != KVM_PFN_ERR_FAULT) {
-			/*
-			 * Keep the mapping if the previous iteration reused
-			 * the existing mapping and didn't create a new one.
-			 */
-			if (new_khva != old_khva)
-				gpc_unmap(new_pfn, new_khva);
-
-			kvm_release_pfn_clean(new_pfn);
-
-			cond_resched();
-		}
-
 		/* We always request a writeable mapping */
-		new_pfn = hva_to_pfn(gpc->uhva, false, false, NULL, true, NULL);
+		new_pfn = hva_to_pfn(uhva, false, false, NULL, true, NULL);
 		if (is_error_noslot_pfn(new_pfn))
-			goto out_error;
+			return -EFAULT;
 
 		/*
-		 * Obtain a new kernel mapping if KVM itself will access the
-		 * pfn.  Note, kmap() and memremap() can both sleep, so this
-		 * too must be done outside of gpc->lock!
+		 * Always obtain a new kernel mapping. Trying to reuse an
+		 * existing one is more complex than it's worth.
 		 */
-		if (new_pfn == gpc->pfn)
-			new_khva = old_khva;
-		else
-			new_khva = gpc_map(new_pfn);
-
+		new_khva = gpc_map(new_pfn);
 		if (!new_khva) {
 			kvm_release_pfn_clean(new_pfn);
-			goto out_error;
+			return -EFAULT;
 		}
 
-		write_lock_irq(&gpc->lock);
+		if (!mmu_notifier_retry_cache(kvm, mmu_seq))
+			break;
 
 		/*
-		 * Other tasks must wait for _this_ refresh to complete before
-		 * attempting to refresh.
+		 * If this iteration "failed" due to an mmu_notifier event,
+		 * release the pfn and unmap the kernel virtual address, and
+		 * loop around again.
 		 */
-		WARN_ON_ONCE(gpc->valid);
-	} while (mmu_notifier_retry_cache(gpc->kvm, mmu_seq));
-
-	gpc->valid = true;
-	gpc->pfn = new_pfn;
-	gpc->khva = new_khva + offset_in_page(gpc->uhva);
+		if (new_pfn != KVM_PFN_ERR_FAULT) {
+			gpc_unmap(new_pfn, new_khva);
+			kvm_release_pfn_clean(new_pfn);
+		}
+	}
 
-	/*
-	 * Put the reference to the _new_ pfn.  The pfn is now tracked by the
-	 * cache and can be safely migrated, swapped, etc... as the cache will
-	 * invalidate any mappings in response to relevant mmu_notifier events.
-	 */
-	kvm_release_pfn_clean(new_pfn);
+	*pfn = new_pfn;
+	*khva = new_khva;
 
 	return 0;
-
-out_error:
-	write_lock_irq(&gpc->lock);
-
-	return -EFAULT;
 }
 
-static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
-			     unsigned long len)
+static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
+			     unsigned long uhva, unsigned long len)
 {
 	unsigned long page_offset = kvm_is_error_gpa(gpa) ?
 		offset_in_page(uhva) : offset_in_page(gpa);
-	bool unmap_old = false;
 	unsigned long old_uhva;
-	kvm_pfn_t old_pfn;
-	bool hva_change = false;
+	kvm_pfn_t old_pfn = KVM_PFN_ERR_FAULT;
 	void *old_khva;
 	int ret;
 
@@ -257,8 +214,9 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 
 	/*
 	 * If another task is refreshing the cache, wait for it to complete.
-	 * There is no guarantee that concurrent refreshes will see the same
-	 * gpa, memslots generation, etc..., so they must be fully serialized.
+	 * This is purely an optimisation, to avoid concurrent mappings from
+	 * hva_to_pfn_retry(), all but one of which will be discarded after
+	 * losing a race to install them in the GPC.
 	 */
 	mutex_lock(&gpc->refresh_lock);
 
@@ -279,7 +237,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 		gpc->uhva = PAGE_ALIGN_DOWN(uhva);
 
 		if (gpc->uhva != old_uhva)
-			hva_change = true;
+			gpc->valid = false;
 	} else {
 		struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
 
@@ -294,7 +252,11 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 
 			if (kvm_is_error_hva(gpc->uhva)) {
 				ret = -EFAULT;
-				goto out;
+
+				gpc->valid = false;
+				gpc->pfn = KVM_PFN_ERR_FAULT;
+				gpc->khva = NULL;
+				goto out_unlock;
 			}
 
 			/*
@@ -302,7 +264,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 			 * HVA may still be the same.
 			 */
 			if (gpc->uhva != old_uhva)
-				hva_change = true;
+				gpc->valid = false;
 		} else {
 			gpc->uhva = old_uhva;
 		}
@@ -315,9 +277,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 	 * If the userspace HVA changed or the PFN was already invalid,
 	 * drop the lock and do the HVA to PFN lookup again.
 	 */
-	if (!gpc->valid || hva_change) {
-		ret = hva_to_pfn_retry(gpc);
-	} else {
+	if (gpc->valid) {
 		/*
 		 * If the HVA→PFN mapping was already valid, don't unmap it.
 		 * But do update gpc->khva because the offset within the page
@@ -325,30 +285,62 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
 		 */
 		gpc->khva = old_khva + page_offset;
 		ret = 0;
-		goto out_unlock;
-	}
 
- out:
-	/*
-	 * Invalidate the cache and purge the pfn/khva if the refresh failed.
-	 * Some/all of the uhva, gpa, and memslot generation info may still be
-	 * valid, leave it as is.
-	 */
-	if (ret) {
+		/* old_pfn must not be unmapped because it was reused. */
+		old_pfn = KVM_PFN_ERR_FAULT;
+	} else {
+		kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
+		unsigned long new_uhva = gpc->uhva;
+		void *new_khva = NULL;
+
+		/*
+		 * Invalidate the cache prior to dropping gpc->lock; the
+		 * gpa=>uhva assets have already been updated and so a
+		 * concurrent check() from a different task may not fail
+		 * the gpa/uhva/generation checks as it should.
+		 */
 		gpc->valid = false;
-		gpc->pfn = KVM_PFN_ERR_FAULT;
-		gpc->khva = NULL;
-	}
 
-	/* Detect a pfn change before dropping the lock! */
-	unmap_old = (old_pfn != gpc->pfn);
+		write_unlock_irq(&gpc->lock);
+
+		ret = hva_to_pfn_retry(gpc->kvm, new_uhva, &new_pfn, &new_khva);
+
+		write_lock_irq(&gpc->lock);
+
+		WARN_ON_ONCE(gpc->valid);
+
+		if (ret || !gpc->active || gpc->uhva != new_uhva) {
+			/*
+			 * On failure or if another change occurred while the
+			 * lock was dropped, just purge the new mapping.
+			 */
+			old_pfn = new_pfn;
+			old_khva = new_khva;
+		} else {
+			old_pfn = gpc->pfn;
+			old_khva = gpc->khva;
+
+			gpc->pfn = new_pfn;
+			gpc->khva = new_khva + offset_in_page(gpc->uhva);
+			gpc->valid = true;
+		}
+
+		/*
+		 * Put the reference to the _new_ pfn. On success, the
+		 * pfn is now tracked by the cache and can safely be
+		 * migrated, swapped, etc. as the cache will invalidate
+		 * any mappings in response to relevant mmu_notifier
+		 * events.
+		 */
+		kvm_release_pfn_clean(new_pfn);
+	}
 
 out_unlock:
 	write_unlock_irq(&gpc->lock);
 
 	mutex_unlock(&gpc->refresh_lock);
 
-	if (unmap_old)
+	if (old_pfn != KVM_PFN_ERR_FAULT)
 		gpc_unmap(old_pfn, old_khva);
 
 	return ret;
-- 
2.39.2

Re: [PATCH v13 21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

[David Woodhouse]

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On Thu, 2024-02-15 at 15:29 +0000, Paul Durrant wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> This function can race with kvm_gpc_deactivate(), which does not take
> the ->refresh_lock. This means kvm_gpc_deactivate() can wipe the ->pfn
> and ->khva fields, and unmap the latter, while hva_to_pfn_retry() has
> temporarily dropped its write lock on gpc->lock.

Let's drop this from your series for now, as it's contentious.

Sean didn't like calling it a 'fix', which I had conceded and reworked
the commit message. It was on the list somewhere, and also in
https://git.infradead.org/users/dwmw2/linux.git/commitdiff/f19755000a7

I *also* think we should do this simpler one:
https://git.infradead.org/users/dwmw2/linux.git/commitdiff/cc69506d19a
... which almost makes the first one unnecessary, but I think we should
do it *anyway* because the rwlock abuse it fixes is kind of awful.

And while we still can't actually *identify* the race condition that
led to a dereference of a NULL gpc->khva while holding the read lock
and gpc->valid and gpc->active both being true... I'll eat my hat if
cleaning up and simplifying the locking (and making it self-contained)
*doesn't* fix it.

But either way, it isn't really part of your series. The only reason it
was tacked on the end was because it would have merge conflicts with
your series, which had been outstanding for months already.

So drop this one, and I'll work this bit out with Sean afterwards.

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Re: [PATCH v13 21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

[Paul Durrant]

On 16/02/2024 13:04, David Woodhouse wrote:
> On Thu, 2024-02-15 at 15:29 +0000, Paul Durrant wrote:
>> From: David Woodhouse <dwmw@amazon.co.uk>
>>
>> This function can race with kvm_gpc_deactivate(), which does not take
>> the ->refresh_lock. This means kvm_gpc_deactivate() can wipe the ->pfn
>> and ->khva fields, and unmap the latter, while hva_to_pfn_retry() has
>> temporarily dropped its write lock on gpc->lock.
> 
> Let's drop this from your series for now, as it's contentious.
> 
> Sean didn't like calling it a 'fix', which I had conceded and reworked
> the commit message. It was on the list somewhere, and also in
> https://git.infradead.org/users/dwmw2/linux.git/commitdiff/f19755000a7
> 
> I *also* think we should do this simpler one:
> https://git.infradead.org/users/dwmw2/linux.git/commitdiff/cc69506d19a
> ... which almost makes the first one unnecessary, but I think we should
> do it *anyway* because the rwlock abuse it fixes is kind of awful.
> 
> And while we still can't actually *identify* the race condition that
> led to a dereference of a NULL gpc->khva while holding the read lock
> and gpc->valid and gpc->active both being true... I'll eat my hat if
> cleaning up and simplifying the locking (and making it self-contained)
> *doesn't* fix it.
> 
> But either way, it isn't really part of your series. The only reason it
> was tacked on the end was because it would have merge conflicts with
> your series, which had been outstanding for months already.
> 
> So drop this one, and I'll work this bit out with Sean afterwards.

Ok. Sean, I assume that since this is the last patch in the series it's 
superfluous for me to post a v14 just for this?

Re: [PATCH v13 21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

[Sean Christopherson]

On Fri, Feb 16, 2024, Paul Durrant wrote:
> On 16/02/2024 13:04, David Woodhouse wrote:
> > On Thu, 2024-02-15 at 15:29 +0000, Paul Durrant wrote:
> > > From: David Woodhouse <dwmw@amazon.co.uk>
> > > 
> > > This function can race with kvm_gpc_deactivate(), which does not take
> > > the ->refresh_lock. This means kvm_gpc_deactivate() can wipe the ->pfn
> > > and ->khva fields, and unmap the latter, while hva_to_pfn_retry() has
> > > temporarily dropped its write lock on gpc->lock.
> > 
> > Let's drop this from your series for now, as it's contentious.
> > 
> > Sean didn't like calling it a 'fix', which I had conceded and reworked
> > the commit message. It was on the list somewhere, and also in
> > https://git.infradead.org/users/dwmw2/linux.git/commitdiff/f19755000a7
> > 
> > I *also* think we should do this simpler one:
> > https://git.infradead.org/users/dwmw2/linux.git/commitdiff/cc69506d19a
> > ... which almost makes the first one unnecessary, but I think we should
> > do it *anyway* because the rwlock abuse it fixes is kind of awful.
> > 
> > And while we still can't actually *identify* the race condition that
> > led to a dereference of a NULL gpc->khva while holding the read lock
> > and gpc->valid and gpc->active both being true... I'll eat my hat if
> > cleaning up and simplifying the locking (and making it self-contained)
> > *doesn't* fix it.

Heh, I'm not taking that bet.

> > But either way, it isn't really part of your series. The only reason it
> > was tacked on the end was because it would have merge conflicts with
> > your series, which had been outstanding for months already.
> > 
> > So drop this one, and I'll work this bit out with Sean afterwards.

FWIW, I'm not opposed to overhauling the gpc locking, I agree it's a mess.  I just
want to proceed slower than I would for a fix, it's a lot to digest.

> Ok. Sean, I assume that since this is the last patch in the series it's
> superfluous for me to post a v14 just for this?

Correct, definitely no need for a new version.

Re: [PATCH v13 21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues

[David Woodhouse]

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On Fri, 2024-02-16 at 07:52 -0800, Sean Christopherson wrote:
> 
> FWIW, I'm not opposed to overhauling the gpc locking, I agree it's a mess.  I just
> want to proceed slower than I would for a fix, it's a lot to digest.

Agreed. I'll do a *really* simple expansion of ->refresh_lock for the fix, and
then cleaning up the rwlock abuse can come later (at the very end of
the series I'm about to post, so it can be ignored for now).

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Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Sean Christopherson]

On Thu, Feb 15, 2024, Paul Durrant wrote:
> David Woodhouse (1):
>   KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues
> 
> Paul Durrant (19):
>   KVM: pfncache: Add a map helper function
>   KVM: pfncache: remove unnecessary exports
>   KVM: x86/xen: mark guest pages dirty with the pfncache lock held
>   KVM: pfncache: add a mark-dirty helper
>   KVM: pfncache: remove KVM_GUEST_USES_PFN usage
>   KVM: pfncache: stop open-coding offset_in_page()
>   KVM: pfncache: include page offset in uhva and use it consistently
>   KVM: pfncache: allow a cache to be activated with a fixed (userspace)
>     HVA
>   KVM: x86/xen: separate initialization of shared_info cache and content
>   KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is
>     set
>   KVM: x86/xen: allow shared_info to be mapped by fixed HVA
>   KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
>   KVM: selftests: map Xen's shared_info page using HVA rather than GFN
>   KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
>   KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA
>     capability
>   KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
>   KVM: x86/xen: don't block on pfncache locks in
>     kvm_xen_set_evtchn_fast()
>   KVM: pfncache: check the need for invalidation under read lock first
>   KVM: x86/xen: allow vcpu_info content to be 'safely' copied
> 
> Sean Christopherson (1):
>   KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
> 
>  Documentation/virt/kvm/api.rst                |  53 ++-
>  arch/s390/kvm/diag.c                          |   2 +-
>  arch/s390/kvm/gaccess.c                       |  14 +-
>  arch/s390/kvm/kvm-s390.c                      |   4 +-
>  arch/s390/kvm/priv.c                          |   4 +-
>  arch/s390/kvm/sigp.c                          |   2 +-
>  arch/x86/kvm/x86.c                            |   7 +-
>  arch/x86/kvm/xen.c                            | 361 +++++++++++------
>  include/linux/kvm_host.h                      |  49 ++-
>  include/linux/kvm_types.h                     |   8 -
>  include/uapi/linux/kvm.h                      |   9 +-
>  .../selftests/kvm/x86_64/xen_shinfo_test.c    |  59 ++-
>  virt/kvm/pfncache.c                           | 382 ++++++++++--------
>  13 files changed, 591 insertions(+), 363 deletions(-)

Except for the read_trylock() patch, just a few nits that I can fixup when
applying, though I'll defeinitely want your eyeballs on the end result as they
tweaks aren't _that_ trivial.

Running tests now, if all goes well I'll push to kvm-x86 within the hour. 

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Paul Durrant]

On 19/02/2024 22:06, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> David Woodhouse (1):
>>    KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues
>>
>> Paul Durrant (19):
>>    KVM: pfncache: Add a map helper function
>>    KVM: pfncache: remove unnecessary exports
>>    KVM: x86/xen: mark guest pages dirty with the pfncache lock held
>>    KVM: pfncache: add a mark-dirty helper
>>    KVM: pfncache: remove KVM_GUEST_USES_PFN usage
>>    KVM: pfncache: stop open-coding offset_in_page()
>>    KVM: pfncache: include page offset in uhva and use it consistently
>>    KVM: pfncache: allow a cache to be activated with a fixed (userspace)
>>      HVA
>>    KVM: x86/xen: separate initialization of shared_info cache and content
>>    KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is
>>      set
>>    KVM: x86/xen: allow shared_info to be mapped by fixed HVA
>>    KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
>>    KVM: selftests: map Xen's shared_info page using HVA rather than GFN
>>    KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
>>    KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA
>>      capability
>>    KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
>>    KVM: x86/xen: don't block on pfncache locks in
>>      kvm_xen_set_evtchn_fast()
>>    KVM: pfncache: check the need for invalidation under read lock first
>>    KVM: x86/xen: allow vcpu_info content to be 'safely' copied
>>
>> Sean Christopherson (1):
>>    KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>>
>>   Documentation/virt/kvm/api.rst                |  53 ++-
>>   arch/s390/kvm/diag.c                          |   2 +-
>>   arch/s390/kvm/gaccess.c                       |  14 +-
>>   arch/s390/kvm/kvm-s390.c                      |   4 +-
>>   arch/s390/kvm/priv.c                          |   4 +-
>>   arch/s390/kvm/sigp.c                          |   2 +-
>>   arch/x86/kvm/x86.c                            |   7 +-
>>   arch/x86/kvm/xen.c                            | 361 +++++++++++------
>>   include/linux/kvm_host.h                      |  49 ++-
>>   include/linux/kvm_types.h                     |   8 -
>>   include/uapi/linux/kvm.h                      |   9 +-
>>   .../selftests/kvm/x86_64/xen_shinfo_test.c    |  59 ++-
>>   virt/kvm/pfncache.c                           | 382 ++++++++++--------
>>   13 files changed, 591 insertions(+), 363 deletions(-)
> 
> Except for the read_trylock() patch, just a few nits that I can fixup when
> applying, though I'll defeinitely want your eyeballs on the end result as they
> tweaks aren't _that_ trivial.
> 
> Running tests now, if all goes well I'll push to kvm-x86 within the hour.

Oh, I read this last and you already made the changes :-) I'll check 
kvm-x86. Thanks.

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Paul Durrant]

On 20/02/2024 09:14, Paul Durrant wrote:
> On 19/02/2024 22:06, Sean Christopherson wrote:
>> On Thu, Feb 15, 2024, Paul Durrant wrote:
>>> David Woodhouse (1):
>>>    KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues
>>>
>>> Paul Durrant (19):
>>>    KVM: pfncache: Add a map helper function
>>>    KVM: pfncache: remove unnecessary exports
>>>    KVM: x86/xen: mark guest pages dirty with the pfncache lock held
>>>    KVM: pfncache: add a mark-dirty helper
>>>    KVM: pfncache: remove KVM_GUEST_USES_PFN usage
>>>    KVM: pfncache: stop open-coding offset_in_page()
>>>    KVM: pfncache: include page offset in uhva and use it consistently
>>>    KVM: pfncache: allow a cache to be activated with a fixed (userspace)
>>>      HVA
>>>    KVM: x86/xen: separate initialization of shared_info cache and 
>>> content
>>>    KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is
>>>      set
>>>    KVM: x86/xen: allow shared_info to be mapped by fixed HVA
>>>    KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
>>>    KVM: selftests: map Xen's shared_info page using HVA rather than GFN
>>>    KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
>>>    KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA
>>>      capability
>>>    KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
>>>    KVM: x86/xen: don't block on pfncache locks in
>>>      kvm_xen_set_evtchn_fast()
>>>    KVM: pfncache: check the need for invalidation under read lock first
>>>    KVM: x86/xen: allow vcpu_info content to be 'safely' copied
>>>
>>> Sean Christopherson (1):
>>>    KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>>>
>>>   Documentation/virt/kvm/api.rst                |  53 ++-
>>>   arch/s390/kvm/diag.c                          |   2 +-
>>>   arch/s390/kvm/gaccess.c                       |  14 +-
>>>   arch/s390/kvm/kvm-s390.c                      |   4 +-
>>>   arch/s390/kvm/priv.c                          |   4 +-
>>>   arch/s390/kvm/sigp.c                          |   2 +-
>>>   arch/x86/kvm/x86.c                            |   7 +-
>>>   arch/x86/kvm/xen.c                            | 361 +++++++++++------
>>>   include/linux/kvm_host.h                      |  49 ++-
>>>   include/linux/kvm_types.h                     |   8 -
>>>   include/uapi/linux/kvm.h                      |   9 +-
>>>   .../selftests/kvm/x86_64/xen_shinfo_test.c    |  59 ++-
>>>   virt/kvm/pfncache.c                           | 382 ++++++++++--------
>>>   13 files changed, 591 insertions(+), 363 deletions(-)
>>
>> Except for the read_trylock() patch, just a few nits that I can fixup 
>> when
>> applying, though I'll defeinitely want your eyeballs on the end result 
>> as they
>> tweaks aren't _that_ trivial.
>>
>> Running tests now, if all goes well I'll push to kvm-x86 within the hour.
> 
> Oh, I read this last and you already made the changes :-) I'll check 
> kvm-x86. Thanks.
> 

I checked the patches you amended. All LGTM and my tests are fine too.

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Sean Christopherson]

On Thu, 15 Feb 2024 15:28:55 +0000, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@amazon.com>
> 
> This series contains a new patch from Sean added since v12 [1]:
> 
> * KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
> 
> This frees up the function name kvm_is_error_gpa() such that it can then be
> re-defined in:
> 
> [...]

*sigh*

I forgot to hit "send" on this yesterday.  But lucky for me, that worked out in
my favor as I needed to rebase on top of kvm/kvm-uapi to avoid pointless conflicts
in the uapi headeres.

So....

Applied to kvm-x86 xen, minus 18 and 19 (trylock stuff) and 21 (locking cleanup
that we're doing elsewhere).

Paul and David, please take (another) look at the end result to make sure you don't
object to any of my tweaks and that I didn't botch anything.

s390 folks, I'm applying/pushing now to get it into -next asap, but I'll make
sure to get acks/reviews on patch 08/21 before I do anything else with this
branch/series.

Thanks!

[01/21] KVM: pfncache: Add a map helper function
        https://github.com/kvm-x86/linux/commit/f39b80e3ff12
[02/21] KVM: pfncache: remove unnecessary exports
        https://github.com/kvm-x86/linux/commit/41496fffc0e1
[03/21] KVM: x86/xen: mark guest pages dirty with the pfncache lock held
        https://github.com/kvm-x86/linux/commit/4438355ec6e1
[04/21] KVM: pfncache: add a mark-dirty helper
        https://github.com/kvm-x86/linux/commit/78b74638eb6d
[05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage
        https://github.com/kvm-x86/linux/commit/a4bff3df5147
[06/21] KVM: pfncache: stop open-coding offset_in_page()
        https://github.com/kvm-x86/linux/commit/53e63e953e14
[07/21] KVM: pfncache: include page offset in uhva and use it consistently
        https://github.com/kvm-x86/linux/commit/406c10962a4c
[08/21] KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
        https://github.com/kvm-x86/linux/commit/9e7325acb3dc
[09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA
        https://github.com/kvm-x86/linux/commit/721f5b0dda78
[10/21] KVM: x86/xen: separate initialization of shared_info cache and content
        https://github.com/kvm-x86/linux/commit/c01c55a34f28
[11/21] KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is set
        https://github.com/kvm-x86/linux/commit/21b99e4d6db6
[12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA
        https://github.com/kvm-x86/linux/commit/10dcbfc46724
[13/21] KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
        https://github.com/kvm-x86/linux/commit/16877dd45f98
[14/21] KVM: selftests: map Xen's shared_info page using HVA rather than GFN
        https://github.com/kvm-x86/linux/commit/95c27ed8619b
[15/21] KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
        https://github.com/kvm-x86/linux/commit/5359bf19a3f0
[16/21] KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability
        https://github.com/kvm-x86/linux/commit/49668ce7e1ae
[17/21] KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
        (not applied)
[18/21] KVM: x86/xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()
        (not applied)
[19/21] KVM: pfncache: check the need for invalidation under read lock first
        https://github.com/kvm-x86/linux/commit/21dadfcd665e
[20/21] KVM: x86/xen: allow vcpu_info content to be 'safely' copied
        https://github.com/kvm-x86/linux/commit/dadeabc3b6fa
[21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues
        (not applied)

--
https://github.com/kvm-x86/linux/tree/next

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Paul Durrant]

On 20/02/2024 15:55, Sean Christopherson wrote:
> On Thu, 15 Feb 2024 15:28:55 +0000, Paul Durrant wrote:
>> From: Paul Durrant <pdurrant@amazon.com>
>>
>> This series contains a new patch from Sean added since v12 [1]:
>>
>> * KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>>
>> This frees up the function name kvm_is_error_gpa() such that it can then be
>> re-defined in:
>>
>> [...]
> 
> *sigh*
> 
> I forgot to hit "send" on this yesterday.  But lucky for me, that worked out in
> my favor as I needed to rebase on top of kvm/kvm-uapi to avoid pointless conflicts
> in the uapi headeres.
> 
> So....
> 
> Applied to kvm-x86 xen, minus 18 and 19 (trylock stuff) and 21 (locking cleanup
> that we're doing elsewhere).
> 

Looks like you meant 17 & 18?

> Paul and David, please take (another) look at the end result to make sure you don't
> object to any of my tweaks and that I didn't botch anything.
> 

What was the issue with 17? It was reasonable clean-up and I'd like to 
keep it even without 18 being applied (and I totally understand your 
reasons for that).

> s390 folks, I'm applying/pushing now to get it into -next asap, but I'll make
> sure to get acks/reviews on patch 08/21 before I do anything else with this
> branch/series.
> 
> Thanks!
> 
> [01/21] KVM: pfncache: Add a map helper function
>          https://github.com/kvm-x86/linux/commit/f39b80e3ff12
> [02/21] KVM: pfncache: remove unnecessary exports
>          https://github.com/kvm-x86/linux/commit/41496fffc0e1
> [03/21] KVM: x86/xen: mark guest pages dirty with the pfncache lock held
>          https://github.com/kvm-x86/linux/commit/4438355ec6e1
> [04/21] KVM: pfncache: add a mark-dirty helper
>          https://github.com/kvm-x86/linux/commit/78b74638eb6d
> [05/21] KVM: pfncache: remove KVM_GUEST_USES_PFN usage
>          https://github.com/kvm-x86/linux/commit/a4bff3df5147
> [06/21] KVM: pfncache: stop open-coding offset_in_page()
>          https://github.com/kvm-x86/linux/commit/53e63e953e14
> [07/21] KVM: pfncache: include page offset in uhva and use it consistently
>          https://github.com/kvm-x86/linux/commit/406c10962a4c
> [08/21] KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>          https://github.com/kvm-x86/linux/commit/9e7325acb3dc
> [09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA
>          https://github.com/kvm-x86/linux/commit/721f5b0dda78
> [10/21] KVM: x86/xen: separate initialization of shared_info cache and content
>          https://github.com/kvm-x86/linux/commit/c01c55a34f28
> [11/21] KVM: x86/xen: re-initialize shared_info if guest (32/64-bit) mode is set
>          https://github.com/kvm-x86/linux/commit/21b99e4d6db6
> [12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA
>          https://github.com/kvm-x86/linux/commit/10dcbfc46724
> [13/21] KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA
>          https://github.com/kvm-x86/linux/commit/16877dd45f98
> [14/21] KVM: selftests: map Xen's shared_info page using HVA rather than GFN
>          https://github.com/kvm-x86/linux/commit/95c27ed8619b
> [15/21] KVM: selftests: re-map Xen's vcpu_info using HVA rather than GPA
>          https://github.com/kvm-x86/linux/commit/5359bf19a3f0
> [16/21] KVM: x86/xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability
>          https://github.com/kvm-x86/linux/commit/49668ce7e1ae
> [17/21] KVM: x86/xen: split up kvm_xen_set_evtchn_fast()
>          (not applied)
> [18/21] KVM: x86/xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()
>          (not applied)
> [19/21] KVM: pfncache: check the need for invalidation under read lock first
>          https://github.com/kvm-x86/linux/commit/21dadfcd665e
> [20/21] KVM: x86/xen: allow vcpu_info content to be 'safely' copied
>          https://github.com/kvm-x86/linux/commit/dadeabc3b6fa
> [21/21] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues
>          (not applied)
> 
> --
> https://github.com/kvm-x86/linux/tree/next

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Sean Christopherson]

On Tue, Feb 20, 2024, Paul Durrant wrote:
> On 20/02/2024 15:55, Sean Christopherson wrote:
> > On Thu, 15 Feb 2024 15:28:55 +0000, Paul Durrant wrote:
> > > From: Paul Durrant <pdurrant@amazon.com>
> > > 
> > > This series contains a new patch from Sean added since v12 [1]:
> > > 
> > > * KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
> > > 
> > > This frees up the function name kvm_is_error_gpa() such that it can then be
> > > re-defined in:
> > > 
> > > [...]
> > 
> > *sigh*
> > 
> > I forgot to hit "send" on this yesterday.  But lucky for me, that worked out in
> > my favor as I needed to rebase on top of kvm/kvm-uapi to avoid pointless conflicts
> > in the uapi headeres.
> > 
> > So....
> > 
> > Applied to kvm-x86 xen, minus 18 and 19 (trylock stuff) and 21 (locking cleanup
> > that we're doing elsewhere).
> > 
> 
> Looks like you meant 17 & 18?

Doh, yes.

> > Paul and David, please take (another) look at the end result to make sure you don't
> > object to any of my tweaks and that I didn't botch anything.
> > 
> 
> What was the issue with 17? It was reasonable clean-up and I'd like to keep
> it even without 18 being applied (and I totally understand your reasons for
> that).

I omitted it purely to avoid creating an unnecessary dependency for the trylock
patch.  That way the trylock patch (or whatever it morphs into) can be applied on
any branch (along with the cleanup), i.e. doesn't need to be taken through kvm-x86/xen.

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[David Woodhouse]

On 20 February 2024 17:15:06 CET, Sean Christopherson <seanjc@google.com> wrote:
>On Tue, Feb 20, 2024, Paul Durrant wrote:
>> On 20/02/2024 15:55, Sean Christopherson wrote:
>> > On Thu, 15 Feb 2024 15:28:55 +0000, Paul Durrant wrote:
>> > > From: Paul Durrant <pdurrant@amazon.com>
>> > > 
>> > > This series contains a new patch from Sean added since v12 [1]:
>> > > 
>> > > * KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>> > > 
>> > > This frees up the function name kvm_is_error_gpa() such that it can then be
>> > > re-defined in:
>> > > 
>> > > [...]
>> > 
>> > *sigh*
>> > 
>> > I forgot to hit "send" on this yesterday.  But lucky for me, that worked out in
>> > my favor as I needed to rebase on top of kvm/kvm-uapi to avoid pointless conflicts
>> > in the uapi headeres.
>> > 
>> > So....
>> > 
>> > Applied to kvm-x86 xen, minus 18 and 19 (trylock stuff) and 21 (locking cleanup
>> > that we're doing elsewhere).
>> > 
>> 
>> Looks like you meant 17 & 18?
>
>Doh, yes.
>
>> > Paul and David, please take (another) look at the end result to make sure you don't
>> > object to any of my tweaks and that I didn't botch anything.
>> > 
>> 
>> What was the issue with 17? It was reasonable clean-up and I'd like to keep
>> it even without 18 being applied (and I totally understand your reasons for
>> that).
>
>I omitted it purely to avoid creating an unnecessary dependency for the trylock
>patch.  That way the trylock patch (or whatever it morphs into) can be applied on
>any branch (along with the cleanup), i.e. doesn't need to be taken through kvm-x86/xen.

What about if (in_atomic() && read_trylock()) return -EAGAIN; else read_lock();

That way we don't have any even theoretical fairness issues because the trylock can fail just *once* which kicks us to the slow path and that'll take the lock normally now.

The condition might not actually be in_atomic() but I'm not working this week and you get the idea.

Re: [PATCH v13 00/21] KVM: xen: update shared_info and vcpu_info handling

[Paul Durrant]

On 20/02/2024 16:15, Sean Christopherson wrote:
> On Tue, Feb 20, 2024, Paul Durrant wrote:
>> On 20/02/2024 15:55, Sean Christopherson wrote:
>>> On Thu, 15 Feb 2024 15:28:55 +0000, Paul Durrant wrote:
>>>> From: Paul Durrant <pdurrant@amazon.com>
>>>>
>>>> This series contains a new patch from Sean added since v12 [1]:
>>>>
>>>> * KVM: s390: Refactor kvm_is_error_gpa() into kvm_is_gpa_in_memslot()
>>>>
>>>> This frees up the function name kvm_is_error_gpa() such that it can then be
>>>> re-defined in:
>>>>
>>>> [...]
>>>
>>> *sigh*
>>>
>>> I forgot to hit "send" on this yesterday.  But lucky for me, that worked out in
>>> my favor as I needed to rebase on top of kvm/kvm-uapi to avoid pointless conflicts
>>> in the uapi headeres.
>>>
>>> So....
>>>
>>> Applied to kvm-x86 xen, minus 18 and 19 (trylock stuff) and 21 (locking cleanup
>>> that we're doing elsewhere).
>>>
>>
>> Looks like you meant 17 & 18?
> 
> Doh, yes.
> 
>>> Paul and David, please take (another) look at the end result to make sure you don't
>>> object to any of my tweaks and that I didn't botch anything.
>>>
>>
>> What was the issue with 17? It was reasonable clean-up and I'd like to keep
>> it even without 18 being applied (and I totally understand your reasons for
>> that).
> 
> I omitted it purely to avoid creating an unnecessary dependency for the trylock
> patch.  That way the trylock patch (or whatever it morphs into) can be applied on
> any branch (along with the cleanup), i.e. doesn't need to be taken through kvm-x86/xen.

Ok, personally I don't see the dependency being an issue. I suspect it 
will be a while before we decide what to do about the locking issue... 
particularly since David is out this week, as he says.