[RFC PATCH v3 34/59] KVM: x86/mmu: Allow non-zero init value for shadow PTE

isaku.yamahata
2021-11-25T00:23:07Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

TDX will run with EPT violation #VEs enabled, which means KVM needs to
set the "suppress #VE" bit in unused PTEs to avoid unintentionally
reflecting not-present EPT violations into the guest.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/mmu/mmu.c | 50 +++++++++++++++++++++++++++++++++++------
arch/x86/kvm/mmu/spte.c | 10 +++++++++
arch/x86/kvm/mmu/spte.h | 2 ++
4 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 583483bb6f71..79ccee8bbc38 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -66,6 +66,7 @@ static __always_inline u64 rsvd_bits(int s, int e)

void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask);
void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only);
+void kvm_mmu_set_spte_init_value(u64 init_value);

void kvm_init_mmu(struct kvm_vcpu *vcpu);
void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 01569913f1f0..510991c2e94e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -623,9 +623,9 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
int level = sptep_to_sp(sptep)->role.level;

if (!spte_has_volatile_bits(old_spte))
- __update_clear_spte_fast(sptep, 0ull);
+ __update_clear_spte_fast(sptep, shadow_init_value);
else
- old_spte = __update_clear_spte_slow(sptep, 0ull);
+ old_spte = __update_clear_spte_slow(sptep, shadow_init_value);

if (!is_shadow_present_pte(old_spte))
return old_spte;
@@ -657,7 +657,7 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
*/
static void mmu_spte_clear_no_track(u64 *sptep)
{
- __update_clear_spte_fast(sptep, 0ull);
+ __update_clear_spte_fast(sptep, shadow_init_value);
}

static u64 mmu_spte_get_lockless(u64 *sptep)
@@ -743,6 +743,42 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
}
}

+static inline void kvm_init_shadow_page(void *page)
+{
+#ifdef CONFIG_X86_64
+ int ign;
+
+ asm volatile (
+ "rep stosq\n\t"
+ : "=c"(ign), "=D"(page)
+ : "a"(shadow_init_value), "c"(4096/8), "D"(page)
+ : "memory"
+ );
+#else
+ BUG();
+#endif
+}
+
+static int mmu_topup_shadow_page_cache(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmu_memory_cache *mc = &vcpu->arch.mmu_shadow_page_cache;
+ int start, end, i, r;
+
+ if (shadow_init_value)
+ start = kvm_mmu_memory_cache_nr_free_objects(mc);
+
+ r = kvm_mmu_topup_memory_cache(mc, PT64_ROOT_MAX_LEVEL);
+ if (r)
+ return r;
+
+ if (shadow_init_value) {
+ end = kvm_mmu_memory_cache_nr_free_objects(mc);
+ for (i = start; i < end; i++)
+ kvm_init_shadow_page(mc->objects[i]);
+ }
+ return 0;
+}
+
static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
{
int r;
@@ -752,8 +788,7 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
if (r)
return r;
- r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache,
- PT64_ROOT_MAX_LEVEL);
+ r = mmu_topup_shadow_page_cache(vcpu);
if (r)
return r;
if (maybe_indirect) {
@@ -3165,7 +3200,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
struct kvm_mmu_page *sp;
int ret = RET_PF_INVALID;
- u64 spte = 0ull;
+ u64 spte = shadow_init_value;
u64 *sptep = NULL;
uint retry_count = 0;

@@ -5584,7 +5619,8 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;

- vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
+ if (!shadow_init_value)
+ vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;

vcpu->arch.mmu = &vcpu->arch.root_mmu;
vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 0c76c45fdb68..bb45e71eb105 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -34,6 +34,7 @@ u64 __read_mostly shadow_mmio_access_mask;
u64 __read_mostly shadow_present_mask;
u64 __read_mostly shadow_me_mask;
u64 __read_mostly shadow_acc_track_mask;
+u64 __read_mostly shadow_init_value;

u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
@@ -221,6 +222,14 @@ u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn)
return new_spte;
}

+void kvm_mmu_set_spte_init_value(u64 init_value)
+{
+ if (WARN_ON(!IS_ENABLED(CONFIG_X86_64) && init_value))
+ init_value = 0;
+ shadow_init_value = init_value;
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_set_spte_init_value);
+
static u8 kvm_get_shadow_phys_bits(void)
{
/*
@@ -365,6 +374,7 @@ void kvm_mmu_reset_all_pte_masks(void)
shadow_present_mask = PT_PRESENT_MASK;
shadow_acc_track_mask = 0;
shadow_me_mask = sme_me_mask;
+ shadow_init_value = 0;

shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITEABLE;
shadow_mmu_writable_mask = DEFAULT_SPTE_MMU_WRITEABLE;
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 56b6dd750fb1..b53b301301dc 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -146,6 +146,8 @@ extern u64 __read_mostly shadow_mmio_access_mask;
extern u64 __read_mostly shadow_present_mask;
extern u64 __read_mostly shadow_me_mask;

+extern u64 __read_mostly shadow_init_value;
+
/*
* SPTEs in MMUs without A/D bits are marked with SPTE_TDP_AD_DISABLED_MASK;
* shadow_acc_track_mask is the set of bits to be cleared in non-accessed
--
2.25.1