[RFC PATCH v3 04/19] KVM: x86: mmu: allow to enable write tracking externally

Maxim Levitsky
2022-04-27T20:04:01Z

This will be used to enable write tracking from nested AVIC code
and can also be used to enable write tracking in GVT-g module
when it actually uses it as opposed to always enabling it,
when the module is compiled in the kernel.

No functional change intended.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/include/asm/kvm_page_track.h | 1 +
arch/x86/kvm/mmu.h | 8 +++++---
arch/x86/kvm/mmu/mmu.c | 17 ++++++++++-------
arch/x86/kvm/mmu/page_track.c | 10 ++++++++--
5 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 636df87542555..fc7df778a3d71 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1254,7 +1254,7 @@ struct kvm_arch {
* is used as one input when determining whether certain memslot
* related allocations are necessary.
*/
- bool shadow_root_allocated;
+ bool mmu_page_tracking_enabled;

#if IS_ENABLED(CONFIG_HYPERV)
hpa_t hv_root_tdp;
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index eb186bc57f6a9..955a5ae07b10e 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -50,6 +50,7 @@ int kvm_page_track_init(struct kvm *kvm);
void kvm_page_track_cleanup(struct kvm *kvm);

bool kvm_page_track_write_tracking_enabled(struct kvm *kvm);
+int kvm_page_track_write_tracking_enable(struct kvm *kvm);
int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot);

void kvm_page_track_free_memslot(struct kvm_memory_slot *slot);
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 671cfeccf04e9..44d15551f7156 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -269,7 +269,7 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
int kvm_mmu_post_init_vm(struct kvm *kvm);
void kvm_mmu_pre_destroy_vm(struct kvm *kvm);

-static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
+static inline bool mmu_page_tracking_enabled(struct kvm *kvm)
{
/*
* Read shadow_root_allocated before related pointers. Hence, threads
@@ -277,9 +277,11 @@ static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
* see the pointers. Pairs with smp_store_release in
* mmu_first_shadow_root_alloc.
*/
- return smp_load_acquire(&kvm->arch.shadow_root_allocated);
+ return smp_load_acquire(&kvm->arch.mmu_page_tracking_enabled);
}

+int mmu_enable_write_tracking(struct kvm *kvm);
+
#ifdef CONFIG_X86_64
static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
#else
@@ -288,7 +290,7 @@ static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }

static inline bool kvm_memslots_have_rmaps(struct kvm *kvm)
{
- return !is_tdp_mmu_enabled(kvm) || kvm_shadow_root_allocated(kvm);
+ return !is_tdp_mmu_enabled(kvm) || mmu_page_tracking_enabled(kvm);
}

static inline gfn_t gfn_to_index(gfn_t gfn, gfn_t base_gfn, int level)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 904f0faff2186..fb744616bf7df 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3389,7 +3389,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
return r;
}

-static int mmu_first_shadow_root_alloc(struct kvm *kvm)
+int mmu_enable_write_tracking(struct kvm *kvm)
{
struct kvm_memslots *slots;
struct kvm_memory_slot *slot;
@@ -3399,21 +3399,20 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
* Check if this is the first shadow root being allocated before
* taking the lock.
*/
- if (kvm_shadow_root_allocated(kvm))
+ if (mmu_page_tracking_enabled(kvm))
return 0;

mutex_lock(&kvm->slots_arch_lock);

/* Recheck, under the lock, whether this is the first shadow root. */
- if (kvm_shadow_root_allocated(kvm))
+ if (mmu_page_tracking_enabled(kvm))
goto out_unlock;

/*
* Check if anything actually needs to be allocated, e.g. all metadata
* will be allocated upfront if TDP is disabled.
*/
- if (kvm_memslots_have_rmaps(kvm) &&
- kvm_page_track_write_tracking_enabled(kvm))
+ if (kvm_memslots_have_rmaps(kvm) && mmu_page_tracking_enabled(kvm))
goto out_success;

for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
@@ -3443,7 +3442,7 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
* all the related pointers are set.
*/
out_success:
- smp_store_release(&kvm->arch.shadow_root_allocated, true);
+ smp_store_release(&kvm->arch.mmu_page_tracking_enabled, true);

out_unlock:
mutex_unlock(&kvm->slots_arch_lock);
@@ -3480,7 +3479,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
}
}

- r = mmu_first_shadow_root_alloc(vcpu->kvm);
+ r = mmu_enable_write_tracking(vcpu->kvm);
if (r)
return r;

@@ -5753,6 +5752,10 @@ int kvm_mmu_init_vm(struct kvm *kvm)
node->track_write = kvm_mmu_pte_write;
node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
kvm_page_track_register_notifier(kvm, node);
+
+ if (IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) || !tdp_enabled)
+ mmu_enable_write_tracking(kvm);
+
return 0;
}

diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 2e09d1b6249f3..8857d629036d7 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -21,10 +21,16 @@

bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)
{
- return IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) ||
- !tdp_enabled || kvm_shadow_root_allocated(kvm);
+ return mmu_page_tracking_enabled(kvm);
}

+int kvm_page_track_write_tracking_enable(struct kvm *kvm)
+{
+ return mmu_enable_write_tracking(kvm);
+}
+EXPORT_SYMBOL_GPL(kvm_page_track_write_tracking_enable);
+
+
void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
{
int i;
--
2.26.3