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KVM: x86/mmu: Remove redundant is_tdp_mmu_enabled check

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This check is redundant because the root shadow page will only be a TDP
MMU page if is_tdp_mmu_enabled() returns true, and is_tdp_mmu_enabled()
never changes for the lifetime of a VM.

It's possible that this check was added for performance reasons but it
is unlikely that it is useful in practice since to_shadow_page() is
cheap. That being said, this patch also caches the return value of
is_tdp_mmu_root() in direct_page_fault() since there's no reason to
duplicate the call so many times, so performance is not a concern.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210617231948.2591431-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack 2021-06-17 23:19:46 +00:00 committed by Paolo Bonzini
parent aa23c0ad14
commit 0b873fd7fb
2 changed files with 7 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/x86/kvm/mmu/mmu.c
View File

@ -3608,7 +3608,7 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
return reserved; return reserved;
} }
if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) if (is_tdp_mmu_root(vcpu->arch.mmu->root_hpa))
leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, &root); leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, &root);
else else
leaf = get_walk(vcpu, addr, sptes, &root); leaf = get_walk(vcpu, addr, sptes, &root);
@ -3780,6 +3780,7 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
bool prefault, int max_level, bool is_tdp) bool prefault, int max_level, bool is_tdp)
{ {
bool is_tdp_mmu_fault = is_tdp_mmu_root(vcpu->arch.mmu->root_hpa);
bool write = error_code & PFERR_WRITE_MASK; bool write = error_code & PFERR_WRITE_MASK;
bool map_writable; bool map_writable;
@ -3792,7 +3793,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (page_fault_handle_page_track(vcpu, error_code, gfn)) if (page_fault_handle_page_track(vcpu, error_code, gfn))
return RET_PF_EMULATE; return RET_PF_EMULATE;
if (!is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) { if (!is_tdp_mmu_fault) {
r = fast_page_fault(vcpu, gpa, error_code); r = fast_page_fault(vcpu, gpa, error_code);
if (r != RET_PF_INVALID) if (r != RET_PF_INVALID)
return r; return r;
@ -3814,7 +3815,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
r = RET_PF_RETRY; r = RET_PF_RETRY;
if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) if (is_tdp_mmu_fault)
read_lock(&vcpu->kvm->mmu_lock); read_lock(&vcpu->kvm->mmu_lock);
else else
write_lock(&vcpu->kvm->mmu_lock); write_lock(&vcpu->kvm->mmu_lock);
@ -3825,7 +3826,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (r) if (r)
goto out_unlock; goto out_unlock;
if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) if (is_tdp_mmu_fault)
r = kvm_tdp_mmu_map(vcpu, gpa, error_code, map_writable, max_level, r = kvm_tdp_mmu_map(vcpu, gpa, error_code, map_writable, max_level,
pfn, prefault); pfn, prefault);
else else
@ -3833,7 +3834,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
prefault, is_tdp); prefault, is_tdp);
out_unlock: out_unlock:
if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) if (is_tdp_mmu_fault)
read_unlock(&vcpu->kvm->mmu_lock); read_unlock(&vcpu->kvm->mmu_lock);
else else
write_unlock(&vcpu->kvm->mmu_lock); write_unlock(&vcpu->kvm->mmu_lock);

4
arch/x86/kvm/mmu/tdp_mmu.h
View File

@ -86,12 +86,10 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; } static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; } static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
static inline bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa) static inline bool is_tdp_mmu_root(hpa_t hpa)
{ {
struct kvm_mmu_page *sp; struct kvm_mmu_page *sp;
if (!is_tdp_mmu_enabled(kvm))
return false;
if (WARN_ON(!VALID_PAGE(hpa))) if (WARN_ON(!VALID_PAGE(hpa)))
return false; return false;