KVM: x86/mmu: Remove redundant is_tdp_mmu_enabled check

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>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7d3e576..10c1c20 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3608,7 +3608,7 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
                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);
        else
                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,
                             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 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))
                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);
                if (r != RET_PF_INVALID)
                        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;
 
-       if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
+       if (is_tdp_mmu_fault)
                read_lock(&vcpu->kvm->mmu_lock);
        else
                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)
                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,
                                    pfn, prefault);
        else
@@ -3833,7 +3834,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
                                 prefault, is_tdp);
 
 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);
        else
                write_unlock(&vcpu->kvm->mmu_lock);

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 78d8a29..f6e0667 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -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_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;
 
-       if (!is_tdp_mmu_enabled(kvm))
-               return false;
        if (WARN_ON(!VALID_PAGE(hpa)))
                return false;