Commit 0b873fd7 authored by David Matlack's avatar David Matlack Committed by Paolo Bonzini
Browse files

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: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Message-Id: <20210617231948.2591431-3-dmatlack@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent aa23c0ad

arch/x86/kvm/mmu/mmu.c

+6 −5
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/mmu/tdp_mmu.h

+1 −3
Original line number Diff line number Diff line
@@ -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;