[PATCH v2 14/25] KVM: x86/mmu: store shadow EFER.NX in the MMU role

Paolo Bonzini
2022-02-21T16:23:22Z

Now that the MMU role is separate from the CPU mode, it can be a
truthful description of the format of the shadow pages. This includes
whether the shadow pages use the NX bit; so force the efer_nx field
of the MMU role when TDP is disabled, and remove the hardcoding it in
the callers of reset_shadow_zero_bits_mask.

In fact, the initialization of reserved SPTE bits can now be made common
to shadow paging and shadow NPT; move it to shadow_mmu_init_context.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu/mmu.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 725aef55c08f..bbb5f50d3dcc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4405,16 +4405,6 @@ static inline u64 reserved_hpa_bits(void)
static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,
struct kvm_mmu *context)
{
- /*
- * KVM uses NX when TDP is disabled to handle a variety of scenarios,
- * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
- * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
- * The iTLB multi-hit workaround can be toggled at any time, so assume
- * NX can be used by any non-nested shadow MMU to avoid having to reset
- * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled.
- */
- bool uses_nx = is_efer_nx(context) || !tdp_enabled;
-
/* @amd adds a check on bit of SPTEs, which KVM shouldn't use anyways. */
bool is_amd = true;
/* KVM doesn't use 2-level page tables for the shadow MMU. */
@@ -4426,7 +4416,8 @@ static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,

shadow_zero_check = &context->shadow_zero_check;
__reset_rsvds_bits_mask(shadow_zero_check, reserved_hpa_bits(),
- context->shadow_root_level, uses_nx,
+ context->shadow_root_level,
+ context->mmu_role.base.efer_nx,
guest_can_use_gbpages(vcpu), is_pse, is_amd);

if (!shadow_me_mask)
@@ -4784,6 +4775,16 @@ kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
else
role.base.level = PT64_ROOT_4LEVEL;

+ /*
+ * KVM forces EFER.NX=1 when TDP is disabled, reflect it in the MMU role.
+ * KVM uses NX when TDP is disabled to handle a variety of scenarios,
+ * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
+ * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
+ * The iTLB multi-hit workaround can be toggled at any time, so assume
+ * NX can be used by any non-nested shadow MMU to avoid having to reset
+ * MMU contexts.
+ */
+ role.base.efer_nx = true;
return role;
}

--
2.31.1