[PATCH 09/18] KVM: x86/mmu: Add a dedicated flag to track if A/D bits are globally enabled

Sean Christopherson
2024-10-11T02:11:11Z

Add a dedicated flag to track if KVM has enabled A/D bits at the module
level, instead of inferring the state based on whether or not the MMU's
shadow_accessed_mask is non-zero. This will allow defining and using
shadow_accessed_mask even when A/D bits aren't used by hardware.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/mmu.c | 6 +++---
arch/x86/kvm/mmu/spte.c | 6 ++++++
arch/x86/kvm/mmu/spte.h | 20 +++++++++-----------
arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
4 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a72ecac63e07..06fb0fd3f87d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3350,7 +3350,7 @@ static bool page_fault_can_be_fast(struct kvm *kvm, struct kvm_page_fault *fault
* by setting the Writable bit, which can be done out of mmu_lock.
*/
if (!fault->present)
- return !kvm_ad_enabled();
+ return !kvm_ad_enabled;

/*
* Note, instruction fetches and writes are mutually exclusive, ignore
@@ -3485,7 +3485,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
* uses A/D bits for non-nested MMUs. Thus, if A/D bits are
* enabled, the SPTE can't be an access-tracked SPTE.
*/
- if (unlikely(!kvm_ad_enabled()) && is_access_track_spte(spte))
+ if (unlikely(!kvm_ad_enabled) && is_access_track_spte(spte))
new_spte = restore_acc_track_spte(new_spte);

/*
@@ -5462,7 +5462,7 @@ kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu,
role.efer_nx = true;
role.smm = cpu_role.base.smm;
role.guest_mode = cpu_role.base.guest_mode;
- role.ad_disabled = !kvm_ad_enabled();
+ role.ad_disabled = !kvm_ad_enabled;
role.level = kvm_mmu_get_tdp_level(vcpu);
role.direct = true;
role.has_4_byte_gpte = false;
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 030813781a63..c9543625dda2 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -24,6 +24,8 @@ static bool __ro_after_init allow_mmio_caching;
module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
EXPORT_SYMBOL_GPL(enable_mmio_caching);

+bool __read_mostly kvm_ad_enabled;
+
u64 __read_mostly shadow_host_writable_mask;
u64 __read_mostly shadow_mmu_writable_mask;
u64 __read_mostly shadow_nx_mask;
@@ -414,6 +416,8 @@ EXPORT_SYMBOL_GPL(kvm_mmu_set_me_spte_mask);

void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
{
+ kvm_ad_enabled = has_ad_bits;
+
shadow_user_mask = VMX_EPT_READABLE_MASK;
shadow_accessed_mask = has_ad_bits ? VMX_EPT_ACCESS_BIT : 0ull;
shadow_dirty_mask = has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
@@ -447,6 +451,8 @@ void kvm_mmu_reset_all_pte_masks(void)
u8 low_phys_bits;
u64 mask;

+ kvm_ad_enabled = true;
+
/*
* If the CPU has 46 or less physical address bits, then set an
* appropriate mask to guard against L1TF attacks. Otherwise, it is
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 574ca9a1fcab..908cb672c4e1 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -167,6 +167,15 @@ static_assert(!(SHADOW_NONPRESENT_VALUE & SPTE_MMU_PRESENT_MASK));
#define SHADOW_NONPRESENT_VALUE 0ULL
#endif

+
+/*
+ * True if A/D bits are supported in hardware and are enabled by KVM. When
+ * enabled, KVM uses A/D bits for all non-nested MMUs. Because L1 can disable
+ * A/D bits in EPTP12, SP and SPTE variants are needed to handle the scenario
+ * where KVM is using A/D bits for L1, but not L2.
+ */
+extern bool __read_mostly kvm_ad_enabled;
+
extern u64 __read_mostly shadow_host_writable_mask;
extern u64 __read_mostly shadow_mmu_writable_mask;
extern u64 __read_mostly shadow_nx_mask;
@@ -285,17 +294,6 @@ static inline bool is_ept_ve_possible(u64 spte)
(spte & VMX_EPT_RWX_MASK) != VMX_EPT_MISCONFIG_WX_VALUE;
}

-/*
- * Returns true if A/D bits are supported in hardware and are enabled by KVM.
- * When enabled, KVM uses A/D bits for all non-nested MMUs. Because L1 can
- * disable A/D bits in EPTP12, SP and SPTE variants are needed to handle the
- * scenario where KVM is using A/D bits for L1, but not L2.
- */
-static inline bool kvm_ad_enabled(void)
-{
- return !!shadow_accessed_mask;
-}
-
static inline bool sp_ad_disabled(struct kvm_mmu_page *sp)
{
return sp->role.ad_disabled;
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index bc9e2f50dc80..f77927b57962 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1075,7 +1075,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
struct kvm_mmu_page *sp, bool shared)
{
- u64 spte = make_nonleaf_spte(sp->spt, !kvm_ad_enabled());
+ u64 spte = make_nonleaf_spte(sp->spt, !kvm_ad_enabled);
int ret = 0;

if (shared) {
@@ -1491,7 +1491,7 @@ static bool tdp_mmu_need_write_protect(struct kvm_mmu_page *sp)
* from level, so it is valid to key off any shadow page to determine if
* write protection is needed for an entire tree.
*/
- return kvm_mmu_page_ad_need_write_protect(sp) || !kvm_ad_enabled();
+ return kvm_mmu_page_ad_need_write_protect(sp) || !kvm_ad_enabled;
}

static void clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
--
2.47.0.rc1.288.g06298d1525-goog