[PATCH v5 0/7] KVM: Guest Memory Pre-Population API

[PATCH v5 0/7] KVM: Guest Memory Pre-Population API

[Paolo Bonzini]

Pre-population has been requested several times to mitigate KVM page faults
during guest boot or after live migration.  It is also required by TDX
before filling in the initial guest memory with measured contents.
Introduce it as a generic API.

Paolo

v4->v5:
- add EIO as possible error
- do not introduce __kvm_mmu_do_page_fault(), instead update stats in callers
- remove goto
- fix commit message to not mention weak symbol
- return error if range->size is 0
- fix comment to explain TDP restriction
- fix guest_test_phys_mem > guest_test_virt_mem case in test

Isaku Yamahata (3):
  KVM: Document KVM_PRE_FAULT_MEMORY ioctl
  KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory
  KVM: selftests: x86: Add test for KVM_PRE_FAULT_MEMORY

Paolo Bonzini (2):
  KVM: x86/mmu: Make kvm_mmu_do_page_fault() return mapped level
  KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()

Sean Christopherson (2):
  KVM: x86/mmu: Bump pf_taken stat only in the "real" page fault handler
  KVM: x86/mmu: Account pf_{fixed,emulate,spurious} in callers of "do
    page fault"

 Documentation/virt/kvm/api.rst                |  55 +++++++
 arch/x86/kvm/Kconfig                          |   1 +
 arch/x86/kvm/mmu/mmu.c                        |  96 +++++++++++-
 arch/x86/kvm/mmu/mmu_internal.h               |  26 +---
 arch/x86/kvm/x86.c                            |   3 +
 include/linux/kvm_host.h                      |   5 +
 include/uapi/linux/kvm.h                      |  10 ++
 tools/include/uapi/linux/kvm.h                |  14 +-
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/pre_fault_memory_test.c     | 146 ++++++++++++++++++
 virt/kvm/Kconfig                              |   3 +
 virt/kvm/kvm_main.c                           |  60 +++++++
 12 files changed, 394 insertions(+), 26 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/pre_fault_memory_test.c

-- 
2.43.0

[PATCH v5 1/7] KVM: Document KVM_PRE_FAULT_MEMORY ioctl

[Paolo Bonzini]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Adds documentation of KVM_PRE_FAULT_MEMORY ioctl. [1]

It populates guest memory.  It doesn't do extra operations on the
underlying technology-specific initialization [2].  For example,
CoCo-related operations won't be performed.  Concretely for TDX, this API
won't invoke TDH.MEM.PAGE.ADD() or TDH.MR.EXTEND().  Vendor-specific APIs
are required for such operations.

The key point is to adapt of vcpu ioctl instead of VM ioctl.  First,
populating guest memory requires vcpu.  If it is VM ioctl, we need to pick
one vcpu somehow.  Secondly, vcpu ioctl allows each vcpu to invoke this
ioctl in parallel.  It helps to scale regarding guest memory size, e.g.,
hundreds of GB.

[1] https://lore.kernel.org/kvm/Zbrj5WKVgMsUFDtb@google.com/
[2] https://lore.kernel.org/kvm/Ze-TJh0BBOWm9spT@google.com/

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-ID: <9a060293c9ad9a78f1d8994cfe1311e818e99257.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Documentation/virt/kvm/api.rst | 55 ++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index a71d91978d9e..d543a5b71d1a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6352,6 +6352,61 @@ a single guest_memfd file, but the bound ranges must not overlap).
 
 See KVM_SET_USER_MEMORY_REGION2 for additional details.
 
+4.143 KVM_PRE_FAULT_MEMORY
+------------------------
+
+:Capability: KVM_CAP_PRE_FAULT_MEMORY
+:Architectures: none
+:Type: vcpu ioctl
+:Parameters: struct kvm_pre_fault_memory (in/out)
+:Returns: 0 if at least one page is processed, < 0 on error
+
+Errors:
+
+  ========== ===============================================================
+  EINVAL     The specified `gpa` and `size` were invalid (e.g. not
+             page aligned, causes an overflow, or size is zero).
+  ENOENT     The specified `gpa` is outside defined memslots.
+  EINTR      An unmasked signal is pending and no page was processed.
+  EFAULT     The parameter address was invalid.
+  EOPNOTSUPP Mapping memory for a GPA is unsupported by the
+             hypervisor, and/or for the current vCPU state/mode.
+  EIO        unexpected error conditions (also causes a WARN)
+  ========== ===============================================================
+
+::
+
+  struct kvm_pre_fault_memory {
+	/* in/out */
+	__u64 gpa;
+	__u64 size;
+	/* in */
+	__u64 flags;
+	__u64 padding[5];
+  };
+
+KVM_PRE_FAULT_MEMORY populates KVM's stage-2 page tables used to map memory
+for the current vCPU state.  KVM maps memory as if the vCPU generated a
+stage-2 read page fault, e.g. faults in memory as needed, but doesn't break
+CoW.  However, KVM does not mark any newly created stage-2 PTE as Accessed.
+
+In some cases, multiple vCPUs might share the page tables.  In this
+case, the ioctl can be called in parallel.
+
+When the ioctl returns, the input values are updated to point to the
+remaining range.  If `size` > 0 on return, the caller can just issue
+the ioctl again with the same `struct kvm_map_memory` argument.
+
+Shadow page tables cannot support this ioctl because they
+are indexed by virtual address or nested guest physical address.
+Calling this ioctl when the guest is using shadow page tables (for
+example because it is running a nested guest with nested page tables)
+will fail with `EOPNOTSUPP` even if `KVM_CHECK_EXTENSION` reports
+the capability to be present.
+
+`flags` must currently be zero.
+
+
 5. The kvm_run structure
 ========================
 
-- 
2.43.0

[PATCH v5 2/7] KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory

[Paolo Bonzini]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Add a new ioctl KVM_PRE_FAULT_MEMORY in the KVM common code. It iterates on the
memory range and calls the arch-specific function.  The implementation is
optional and enabled by a Kconfig symbol.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Message-ID: <819322b8f25971f2b9933bfa4506e618508ad782.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/linux/kvm_host.h |  5 ++++
 include/uapi/linux/kvm.h | 10 +++++++
 virt/kvm/Kconfig         |  3 ++
 virt/kvm/kvm_main.c      | 60 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 78 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7b57878c8c18..c3c922bf077f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2477,4 +2477,9 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t gfn, void __user *src, long npages
 void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
 #endif
 
+#ifdef CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY
+long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+				    struct kvm_pre_fault_memory *range);
+#endif
+
 #endif
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d03842abae57..e5af8c692dc0 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -917,6 +917,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_MEMORY_ATTRIBUTES 233
 #define KVM_CAP_GUEST_MEMFD 234
 #define KVM_CAP_VM_TYPES 235
+#define KVM_CAP_PRE_FAULT_MEMORY 236
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1548,4 +1549,13 @@ struct kvm_create_guest_memfd {
 	__u64 reserved[6];
 };
 
+#define KVM_PRE_FAULT_MEMORY	_IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory)
+
+struct kvm_pre_fault_memory {
+	__u64 gpa;
+	__u64 size;
+	__u64 flags;
+	__u64 padding[5];
+};
+
 #endif /* __LINUX_KVM_H */
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 754c6c923427..b14e14cdbfb9 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -67,6 +67,9 @@ config HAVE_KVM_INVALID_WAKEUPS
 config KVM_GENERIC_DIRTYLOG_READ_PROTECT
        bool
 
+config KVM_GENERIC_PRE_FAULT_MEMORY
+       bool
+
 config KVM_COMPAT
        def_bool y
        depends on KVM && COMPAT && !(S390 || ARM64 || RISCV)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8e422c2c9450..f817ec66c85f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4373,6 +4373,52 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
 	return fd;
 }
 
+#ifdef CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY
+static int kvm_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+				     struct kvm_pre_fault_memory *range)
+{
+	int idx;
+	long r;
+	u64 full_size;
+
+	if (range->flags)
+		return -EINVAL;
+
+	if (!PAGE_ALIGNED(range->gpa) ||
+	    !PAGE_ALIGNED(range->size) ||
+	    range->gpa + range->size <= range->gpa)
+		return -EINVAL;
+
+	vcpu_load(vcpu);
+	idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+	full_size = range->size;
+	do {
+		if (signal_pending(current)) {
+			r = -EINTR;
+			break;
+		}
+
+		r = kvm_arch_vcpu_pre_fault_memory(vcpu, range);
+		if (WARN_ON_ONCE(r == 0 || r == -EIO))
+			break;
+
+		if (r < 0)
+			break;
+
+		range->size -= r;
+		range->gpa += r;
+		cond_resched();
+	} while (range->size);
+
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
+	vcpu_put(vcpu);
+
+	/* Return success if at least one page was mapped successfully.  */
+	return full_size == range->size ? r : 0;
+}
+#endif
+
 static long kvm_vcpu_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -4573,6 +4619,20 @@ static long kvm_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
 		break;
 	}
+#ifdef CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY
+	case KVM_PRE_FAULT_MEMORY: {
+		struct kvm_pre_fault_memory range;
+
+		r = -EFAULT;
+		if (copy_from_user(&range, argp, sizeof(range)))
+			break;
+		r = kvm_vcpu_pre_fault_memory(vcpu, &range);
+		/* Pass back leftover range. */
+		if (copy_to_user(argp, &range, sizeof(range)))
+			r = -EFAULT;
+		break;
+	}
+#endif
 	default:
 		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 	}
-- 
2.43.0

Re: [PATCH v5 2/7] KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory

[Anish Moorthy]

On Wed, Jul 10, 2024 at 10:41 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> +       if (!PAGE_ALIGNED(range->gpa) ||
> +           !PAGE_ALIGNED(range->size) ||
> ...
> +               return -EINVAL;

If 'gpa' and 'size' must be page-aligned anyways, doesn't it make
sense to just take a 'gfn' and 'num_pages'  and eliminate this error
condition?

Re: [PATCH v5 2/7] KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory

[Sean Christopherson]

On Wed, Jul 10, 2024, Anish Moorthy wrote:
> On Wed, Jul 10, 2024 at 10:41 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
> >
> > +       if (!PAGE_ALIGNED(range->gpa) ||
> > +           !PAGE_ALIGNED(range->size) ||
> > ...
> > +               return -EINVAL;
> 
> If 'gpa' and 'size' must be page-aligned anyways, doesn't it make
> sense to just take a 'gfn' and 'num_pages'  and eliminate this error
> condition?

The downside is that taking gfn+num_pages prevents supporting sub-page pre-faulting
in the future.  I highly doubt that sub-page mappings will ever be a thing in KVM,
but two PAGE_ALIGNED() checks is super cheap, so it's soft of a "why not?" scenario.

Re: [PATCH v5 2/7] KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory

[Paolo Bonzini]

On Wed, Jul 10, 2024 at 11:56 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Wed, Jul 10, 2024, Anish Moorthy wrote:
> > On Wed, Jul 10, 2024 at 10:41 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
> > >
> > > +       if (!PAGE_ALIGNED(range->gpa) ||
> > > +           !PAGE_ALIGNED(range->size) ||
> > > ...
> > > +               return -EINVAL;
> >
> > If 'gpa' and 'size' must be page-aligned anyways, doesn't it make
> > sense to just take a 'gfn' and 'num_pages'  and eliminate this error
> > condition?
>
> The downside is that taking gfn+num_pages prevents supporting sub-page pre-faulting
> in the future.  I highly doubt that sub-page mappings will ever be a thing in KVM,
> but two PAGE_ALIGNED() checks is super cheap, so it's soft of a "why not?" scenario.

With ARM having multiple page sizes, and not necessarily the same size
in host and guest, using a gfn argument is also unnecessarily
confusing.

Paolo

[PATCH v5 3/7] KVM: x86/mmu: Bump pf_taken stat only in the "real" page fault handler

[Paolo Bonzini]

From: Sean Christopherson <seanjc@google.com>

Account stat.pf_taken in kvm_mmu_page_fault(), i.e. the actual page fault
handler, instead of conditionally bumping it in kvm_mmu_do_page_fault().
The "real" page fault handler is the only path that should ever increment
the number of taken page faults, as all other paths that "do page fault"
are by definition not handling faults that occurred in the guest.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c          | 2 ++
 arch/x86/kvm/mmu/mmu_internal.h | 8 --------
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8b64f31e13be..aa437aacf55f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5925,6 +5925,8 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 	}
 
 	if (r == RET_PF_INVALID) {
+		vcpu->stat.pf_taken++;
+
 		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa, error_code, false,
 					  &emulation_type);
 		if (KVM_BUG_ON(r == RET_PF_INVALID, vcpu->kvm))
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index ce2fcd19ba6b..8efd31b3856b 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -318,14 +318,6 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		fault.slot = kvm_vcpu_gfn_to_memslot(vcpu, fault.gfn);
 	}
 
-	/*
-	 * Async #PF "faults", a.k.a. prefetch faults, are not faults from the
-	 * guest perspective and have already been counted at the time of the
-	 * original fault.
-	 */
-	if (!prefetch)
-		vcpu->stat.pf_taken++;
-
 	if (IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) && fault.is_tdp)
 		r = kvm_tdp_page_fault(vcpu, &fault);
 	else
-- 
2.43.0

[PATCH v5 4/7] KVM: x86/mmu: Account pf_{fixed,emulate,spurious} in callers of "do page fault"

[Paolo Bonzini]

From: Sean Christopherson <seanjc@google.com>

Move the accounting of the result of kvm_mmu_do_page_fault() to its
callers, as only pf_fixed is common to guest page faults and async #PFs,
and upcoming support KVM_PRE_FAULT_MEMORY won't bump _any_ stats.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c          | 19 ++++++++++++++++++-
 arch/x86/kvm/mmu/mmu_internal.h | 13 -------------
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index aa437aacf55f..8c2c5c0afba1 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4291,7 +4291,16 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 	      work->arch.cr3 != kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu))
 		return;
 
-	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code, true, NULL);
+	r = kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code,
+				  true, NULL);
+
+	/*
+	 * Account fixed page faults, otherwise they'll never be counted, but
+	 * ignore stats for all other return times.  Page-ready "faults" aren't
+	 * truly spurious and never trigger emulation
+	 */
+	if (r == RET_PF_FIXED)
+		vcpu->stat.pf_fixed++;
 }
 
 static inline u8 kvm_max_level_for_order(int order)
@@ -5935,6 +5944,14 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 
 	if (r < 0)
 		return r;
+
+	if (r == RET_PF_FIXED)
+		vcpu->stat.pf_fixed++;
+	else if (r == RET_PF_EMULATE)
+		vcpu->stat.pf_emulate++;
+	else if (r == RET_PF_SPURIOUS)
+		vcpu->stat.pf_spurious++;
+
 	if (r != RET_PF_EMULATE)
 		return 1;
 
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 8efd31b3856b..444f55a5eed7 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -337,19 +337,6 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	if (fault.write_fault_to_shadow_pgtable && emulation_type)
 		*emulation_type |= EMULTYPE_WRITE_PF_TO_SP;
 
-	/*
-	 * Similar to above, prefetch faults aren't truly spurious, and the
-	 * async #PF path doesn't do emulation.  Do count faults that are fixed
-	 * by the async #PF handler though, otherwise they'll never be counted.
-	 */
-	if (r == RET_PF_FIXED)
-		vcpu->stat.pf_fixed++;
-	else if (prefetch)
-		;
-	else if (r == RET_PF_EMULATE)
-		vcpu->stat.pf_emulate++;
-	else if (r == RET_PF_SPURIOUS)
-		vcpu->stat.pf_spurious++;
 	return r;
 }
 
-- 
2.43.0

[PATCH v5 5/7] KVM: x86/mmu: Make kvm_mmu_do_page_fault() return mapped level

[Paolo Bonzini]

The guest memory population logic will need to know what page size or level
(4K, 2M, ...) is mapped.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-ID: <eabc3f3e5eb03b370cadf6e1901ea34d7a020adc.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c          | 4 ++--
 arch/x86/kvm/mmu/mmu_internal.h | 5 ++++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8c2c5c0afba1..152b30fa22ad 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4292,7 +4292,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 		return;
 
 	r = kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code,
-				  true, NULL);
+				  true, NULL, NULL);
 
 	/*
 	 * Account fixed page faults, otherwise they'll never be counted, but
@@ -5937,7 +5937,7 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 		vcpu->stat.pf_taken++;
 
 		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa, error_code, false,
-					  &emulation_type);
+					  &emulation_type, NULL);
 		if (KVM_BUG_ON(r == RET_PF_INVALID, vcpu->kvm))
 			return -EIO;
 	}
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 444f55a5eed7..1721d97743e9 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -288,7 +288,8 @@ static inline void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
 }
 
 static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
-					u64 err, bool prefetch, int *emulation_type)
+					u64 err, bool prefetch,
+					int *emulation_type, u8 *level)
 {
 	struct kvm_page_fault fault = {
 		.addr = cr2_or_gpa,
@@ -336,6 +337,8 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 
 	if (fault.write_fault_to_shadow_pgtable && emulation_type)
 		*emulation_type |= EMULTYPE_WRITE_PF_TO_SP;
+	if (level)
+		*level = fault.goal_level;
 
 	return r;
 }
-- 
2.43.0

[PATCH v5 6/7] KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()

[Paolo Bonzini]

Wire KVM_PRE_FAULT_MEMORY ioctl to __kvm_mmu_do_page_fault() to populate guest
memory.  It can be called right after KVM_CREATE_VCPU creates a vCPU,
since at that point kvm_mmu_create() and kvm_init_mmu() are called and
the vCPU is ready to invoke the KVM page fault handler.

The helper function kvm_mmu_map_tdp_page take care of the logic to
process RET_PF_* return values and convert them to success or errno.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-ID: <9b866a0ae7147f96571c439e75429a03dcb659b6.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/Kconfig   |  1 +
 arch/x86/kvm/mmu/mmu.c | 73 ++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c     |  3 ++
 3 files changed, 77 insertions(+)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 80e5afde69f4..4287a8071a3a 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -44,6 +44,7 @@ config KVM
 	select KVM_VFIO
 	select HAVE_KVM_PM_NOTIFIER if PM
 	select KVM_GENERIC_HARDWARE_ENABLING
+	select KVM_GENERIC_PRE_FAULT_MEMORY
 	select KVM_WERROR if WERROR
 	help
 	  Support hosting fully virtualized guest machines using hardware
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 152b30fa22ad..4e0e9963066f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4709,6 +4709,79 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	return direct_page_fault(vcpu, fault);
 }
 
+static int kvm_tdp_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code,
+			    u8 *level)
+{
+	int r;
+
+	/*
+	 * Restrict to TDP page fault, since that's the only case where the MMU
+	 * is indexed by GPA.
+	 */
+	if (vcpu->arch.mmu->page_fault != kvm_tdp_page_fault)
+		return -EOPNOTSUPP;
+
+	do {
+		if (signal_pending(current))
+			return -EINTR;
+		cond_resched();
+		r = kvm_mmu_do_page_fault(vcpu, gpa, error_code, true, NULL, level);
+	} while (r == RET_PF_RETRY);
+
+	if (r < 0)
+		return r;
+
+	switch (r) {
+	case RET_PF_FIXED:
+	case RET_PF_SPURIOUS:
+		return 0;
+
+	case RET_PF_EMULATE:
+		return -ENOENT;
+
+	case RET_PF_RETRY:
+	case RET_PF_CONTINUE:
+	case RET_PF_INVALID:
+	default:
+		WARN_ONCE(1, "could not fix page fault during prefault");
+		return -EIO;
+	}
+}
+
+long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+				    struct kvm_pre_fault_memory *range)
+{
+	u64 error_code = PFERR_GUEST_FINAL_MASK;
+	u8 level = PG_LEVEL_4K;
+	u64 end;
+	int r;
+
+	/*
+	 * reload is efficient when called repeatedly, so we can do it on
+	 * every iteration.
+	 */
+	kvm_mmu_reload(vcpu);
+
+	if (kvm_arch_has_private_mem(vcpu->kvm) &&
+	    kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa)))
+		error_code |= PFERR_PRIVATE_ACCESS;
+
+	/*
+	 * Shadow paging uses GVA for kvm page fault, so restrict to
+	 * two-dimensional paging.
+	 */
+	r = kvm_tdp_map_page(vcpu, range->gpa, error_code, &level);
+	if (r < 0)
+		return r;
+
+	/*
+	 * If the mapping that covers range->gpa can use a huge page, it
+	 * may start below it or end after range->gpa + range->size.
+	 */
+	end = (range->gpa & KVM_HPAGE_MASK(level)) + KVM_HPAGE_SIZE(level);
+	return min(range->size, end - range->gpa);
+}
+
 static void nonpaging_init_context(struct kvm_mmu *context)
 {
 	context->page_fault = nonpaging_page_fault;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ba0ad76f53bc..a6968eadd418 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4705,6 +4705,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MEMORY_FAULT_INFO:
 		r = 1;
 		break;
+	case KVM_CAP_PRE_FAULT_MEMORY:
+		r = tdp_enabled;
+		break;
 	case KVM_CAP_EXIT_HYPERCALL:
 		r = KVM_EXIT_HYPERCALL_VALID_MASK;
 		break;
-- 
2.43.0

Re: [PATCH v5 6/7] KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()

[Binbin Wu]

On 7/11/2024 1:40 AM, Paolo Bonzini wrote:
> Wire KVM_PRE_FAULT_MEMORY ioctl to __kvm_mmu_do_page_fault() to populate guest

__kvm_mmu_do_page_fault() -> kvm_mmu_do_page_fault()



> memory.  It can be called right after KVM_CREATE_VCPU creates a vCPU,
> since at that point kvm_mmu_create() and kvm_init_mmu() are called and
> the vCPU is ready to invoke the KVM page fault handler.
>
> The helper function kvm_mmu_map_tdp_page take care of the logic to

kvm_mmu_map_tdp_page -> kvm_tdp_map_page()?



> process RET_PF_* return values and convert them to success or errno.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Message-ID: <9b866a0ae7147f96571c439e75429a03dcb659b6.1712785629.git.isaku.yamahata@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   arch/x86/kvm/Kconfig   |  1 +
>   arch/x86/kvm/mmu/mmu.c | 73 ++++++++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/x86.c     |  3 ++
>   3 files changed, 77 insertions(+)
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 80e5afde69f4..4287a8071a3a 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -44,6 +44,7 @@ config KVM
>   	select KVM_VFIO
>   	select HAVE_KVM_PM_NOTIFIER if PM
>   	select KVM_GENERIC_HARDWARE_ENABLING
> +	select KVM_GENERIC_PRE_FAULT_MEMORY
>   	select KVM_WERROR if WERROR
>   	help
>   	  Support hosting fully virtualized guest machines using hardware
[...]
> index ba0ad76f53bc..a6968eadd418 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4705,6 +4705,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_MEMORY_FAULT_INFO:
>   		r = 1;
>   		break;
> +	case KVM_CAP_PRE_FAULT_MEMORY:
> +		r = tdp_enabled;
> +		break;
If !CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY, this should return 0.

>   	case KVM_CAP_EXIT_HYPERCALL:
>   		r = KVM_EXIT_HYPERCALL_VALID_MASK;
>   		break;

Re: [PATCH v5 6/7] KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()

[Paolo Bonzini]

On Thu, Jul 11, 2024 at 7:37 AM Binbin Wu <binbin.wu@linux.intel.com> wrote:
> On 7/11/2024 1:40 AM, Paolo Bonzini wrote:
> > Wire KVM_PRE_FAULT_MEMORY ioctl to __kvm_mmu_do_page_fault() to populate guest
>
> __kvm_mmu_do_page_fault() -> kvm_mmu_do_page_fault()
>
> > memory.  It can be called right after KVM_CREATE_VCPU creates a vCPU,
> > since at that point kvm_mmu_create() and kvm_init_mmu() are called and
> > the vCPU is ready to invoke the KVM page fault handler.
> >
> > The helper function kvm_mmu_map_tdp_page take care of the logic to
>
> kvm_mmu_map_tdp_page -> kvm_tdp_map_page()?

Yes, will fix.

> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index 80e5afde69f4..4287a8071a3a 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -44,6 +44,7 @@ config KVM
> >       select KVM_VFIO
> >       select HAVE_KVM_PM_NOTIFIER if PM
> >       select KVM_GENERIC_HARDWARE_ENABLING
> > +     select KVM_GENERIC_PRE_FAULT_MEMORY
> >       select KVM_WERROR if WERROR
> >       help
> >         Support hosting fully virtualized guest machines using hardware
> [...]
> > index ba0ad76f53bc..a6968eadd418 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4705,6 +4705,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >       case KVM_CAP_MEMORY_FAULT_INFO:
> >               r = 1;
> >               break;
> > +     case KVM_CAP_PRE_FAULT_MEMORY:
> > +             r = tdp_enabled;
> > +             break;
> If !CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY, this should return 0.

This is x86-specific code and it CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY
is always selected by CONFIG_KVM on x86 (that is, it does not depend
on TDX or anything else).

Paolo

[PATCH v5 7/7] KVM: selftests: x86: Add test for KVM_PRE_FAULT_MEMORY

[Paolo Bonzini]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Add a test case to exercise KVM_PRE_FAULT_MEMORY and run the guest to access the
pre-populated area.  It tests KVM_PRE_FAULT_MEMORY ioctl for KVM_X86_DEFAULT_VM
and KVM_X86_SW_PROTECTED_VM.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-ID: <32427791ef42e5efaafb05d2ac37fa4372715f47.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tools/include/uapi/linux/kvm.h                |  14 +-
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/pre_fault_memory_test.c     | 146 ++++++++++++++++++
 3 files changed, 159 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/pre_fault_memory_test.c

diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
index ea32b101b999..e5af8c692dc0 100644
--- a/tools/include/uapi/linux/kvm.h
+++ b/tools/include/uapi/linux/kvm.h
@@ -917,6 +917,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_MEMORY_ATTRIBUTES 233
 #define KVM_CAP_GUEST_MEMFD 234
 #define KVM_CAP_VM_TYPES 235
+#define KVM_CAP_PRE_FAULT_MEMORY 236
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1221,9 +1222,9 @@ struct kvm_vfio_spapr_tce {
 /* Available with KVM_CAP_SPAPR_RESIZE_HPT */
 #define KVM_PPC_RESIZE_HPT_PREPARE _IOR(KVMIO, 0xad, struct kvm_ppc_resize_hpt)
 #define KVM_PPC_RESIZE_HPT_COMMIT  _IOR(KVMIO, 0xae, struct kvm_ppc_resize_hpt)
-/* Available with KVM_CAP_PPC_RADIX_MMU or KVM_CAP_PPC_MMU_HASH_V3 */
+/* Available with KVM_CAP_PPC_MMU_RADIX or KVM_CAP_PPC_MMU_HASH_V3 */
 #define KVM_PPC_CONFIGURE_V3_MMU  _IOW(KVMIO,  0xaf, struct kvm_ppc_mmuv3_cfg)
-/* Available with KVM_CAP_PPC_RADIX_MMU */
+/* Available with KVM_CAP_PPC_MMU_RADIX */
 #define KVM_PPC_GET_RMMU_INFO	  _IOW(KVMIO,  0xb0, struct kvm_ppc_rmmu_info)
 /* Available with KVM_CAP_PPC_GET_CPU_CHAR */
 #define KVM_PPC_GET_CPU_CHAR	  _IOR(KVMIO,  0xb1, struct kvm_ppc_cpu_char)
@@ -1548,4 +1549,13 @@ struct kvm_create_guest_memfd {
 	__u64 reserved[6];
 };
 
+#define KVM_PRE_FAULT_MEMORY	_IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory)
+
+struct kvm_pre_fault_memory {
+	__u64 gpa;
+	__u64 size;
+	__u64 flags;
+	__u64 padding[5];
+};
+
 #endif /* __LINUX_KVM_H */
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index ce8ff8e8ce3a..e915d4ae1793 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -145,6 +145,7 @@ TEST_GEN_PROGS_x86_64 += set_memory_region_test
 TEST_GEN_PROGS_x86_64 += steal_time
 TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test
 TEST_GEN_PROGS_x86_64 += system_counter_offset_test
+TEST_GEN_PROGS_x86_64 += pre_fault_memory_test
 
 # Compiled outputs used by test targets
 TEST_GEN_PROGS_EXTENDED_x86_64 += x86_64/nx_huge_pages_test
diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c
new file mode 100644
index 000000000000..0350a8896a2f
--- /dev/null
+++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024, Intel, Inc
+ *
+ * Author:
+ * Isaku Yamahata <isaku.yamahata at gmail.com>
+ */
+#include <linux/sizes.h>
+
+#include <test_util.h>
+#include <kvm_util.h>
+#include <processor.h>
+
+/* Arbitrarily chosen values */
+#define TEST_SIZE		(SZ_2M + PAGE_SIZE)
+#define TEST_NPAGES		(TEST_SIZE / PAGE_SIZE)
+#define TEST_SLOT		10
+
+static void guest_code(uint64_t base_gpa)
+{
+	volatile uint64_t val __used;
+	int i;
+
+	for (i = 0; i < TEST_NPAGES; i++) {
+		uint64_t *src = (uint64_t *)(base_gpa + i * PAGE_SIZE);
+
+		val = *src;
+	}
+
+	GUEST_DONE();
+}
+
+static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 gpa, u64 size,
+			     u64 left)
+{
+	struct kvm_pre_fault_memory range = {
+		.gpa = gpa,
+		.size = size,
+		.flags = 0,
+	};
+	u64 prev;
+	int ret, save_errno;
+
+	do {
+		prev = range.size;
+		ret = __vcpu_ioctl(vcpu, KVM_PRE_FAULT_MEMORY, &range);
+		save_errno = errno;
+		TEST_ASSERT((range.size < prev) ^ (ret < 0),
+			    "%sexpecting range.size to change on %s",
+			    ret < 0 ? "not " : "",
+			    ret < 0 ? "failure" : "success");
+	} while (ret >= 0 ? range.size : save_errno == EINTR);
+
+	TEST_ASSERT(range.size == left,
+		    "Completed with %lld bytes left, expected %" PRId64,
+		    range.size, left);
+
+	if (left == 0)
+		__TEST_ASSERT_VM_VCPU_IOCTL(!ret, "KVM_PRE_FAULT_MEMORY", ret, vcpu->vm);
+	else
+		/* No memory slot causes RET_PF_EMULATE. it results in -ENOENT. */
+		__TEST_ASSERT_VM_VCPU_IOCTL(ret && save_errno == ENOENT,
+					    "KVM_PRE_FAULT_MEMORY", ret, vcpu->vm);
+}
+
+static void __test_pre_fault_memory(unsigned long vm_type, bool private)
+{
+	const struct vm_shape shape = {
+		.mode = VM_MODE_DEFAULT,
+		.type = vm_type,
+	};
+	struct kvm_vcpu *vcpu;
+	struct kvm_run *run;
+	struct kvm_vm *vm;
+	struct ucall uc;
+
+	uint64_t guest_test_phys_mem;
+	uint64_t guest_test_virt_mem;
+	uint64_t alignment, guest_page_size;
+
+	vm = vm_create_shape_with_one_vcpu(shape, &vcpu, guest_code);
+
+	alignment = guest_page_size = vm_guest_mode_params[VM_MODE_DEFAULT].page_size;
+	guest_test_phys_mem = (vm->max_gfn - TEST_NPAGES) * guest_page_size;
+#ifdef __s390x__
+	alignment = max(0x100000UL, guest_page_size);
+#else
+	alignment = SZ_2M;
+#endif
+	guest_test_phys_mem = align_down(guest_test_phys_mem, alignment);
+	guest_test_virt_mem = guest_test_phys_mem & ((1ULL << (vm->va_bits - 1)) - 1);
+
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+				    guest_test_phys_mem, TEST_SLOT, TEST_NPAGES,
+				    private ? KVM_MEM_GUEST_MEMFD : 0);
+	virt_map(vm, guest_test_virt_mem, guest_test_phys_mem, TEST_NPAGES);
+
+	if (private)
+		vm_mem_set_private(vm, guest_test_phys_mem, TEST_SIZE);
+	pre_fault_memory(vcpu, guest_test_phys_mem, SZ_2M, 0);
+	pre_fault_memory(vcpu, guest_test_phys_mem + SZ_2M, PAGE_SIZE * 2, PAGE_SIZE);
+	pre_fault_memory(vcpu, guest_test_phys_mem + TEST_SIZE, PAGE_SIZE, PAGE_SIZE);
+
+	vcpu_args_set(vcpu, 1, guest_test_virt_mem);
+	vcpu_run(vcpu);
+
+	run = vcpu->run;
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+		    "Wanted KVM_EXIT_IO, got exit reason: %u (%s)",
+		    run->exit_reason, exit_reason_str(run->exit_reason));
+
+	switch (get_ucall(vcpu, &uc)) {
+	case UCALL_ABORT:
+		REPORT_GUEST_ASSERT(uc);
+		break;
+	case UCALL_DONE:
+		break;
+	default:
+		TEST_FAIL("Unknown ucall 0x%lx.", uc.cmd);
+		break;
+	}
+
+	kvm_vm_free(vm);
+}
+
+static void test_pre_fault_memory(unsigned long vm_type, bool private)
+{
+	if (vm_type && !(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type))) {
+		pr_info("Skipping tests for vm_type 0x%lx\n", vm_type);
+		return;
+	}
+
+	__test_pre_fault_memory(vm_type, private);
+}
+
+int main(int argc, char *argv[])
+{
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
+
+	test_pre_fault_memory(0, false);
+#ifdef __x86_64__
+	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, false);
+	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, true);
+#endif
+	return 0;
+}
-- 
2.43.0