[PATCH] KVM: x86/mmu: Refactor slot null check in kvm_mmu_hugepage_adjust

[PATCH] KVM: x86/mmu: Refactor slot null check in kvm_mmu_hugepage_adjust

[David Matlack]

The current code is correct but relies on is_error_noslot_pfn() to
ensure slot is not null. The only reason is_error_noslot_pfn() was
checked instead is because we did not have the slot before
commit 6574422f913e ("KVM: x86/mmu: Pass the memslot around via struct
kvm_page_fault") and looking up the memslot is expensive.

Now that the slot is available, explicitly check if it's null and
get rid of the redundant is_error_noslot_pfn() check.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4853c033e6ce..9b5424bcb173 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2925,10 +2925,10 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	if (unlikely(fault->max_level == PG_LEVEL_4K))
 		return;
 
-	if (is_error_noslot_pfn(fault->pfn) || kvm_is_reserved_pfn(fault->pfn))
+	if (!slot || kvm_slot_dirty_track_enabled(slot))
 		return;
 
-	if (kvm_slot_dirty_track_enabled(slot))
+	if (kvm_is_reserved_pfn(fault->pfn))
 		return;
 
 	/*
-- 
2.33.0.rc2.250.ged5fa647cd-goog

Re: [PATCH] KVM: x86/mmu: Refactor slot null check in kvm_mmu_hugepage_adjust

[Sean Christopherson]

On Tue, Aug 24, 2021, David Matlack wrote:
> The current code is correct but relies on is_error_noslot_pfn() to
> ensure slot is not null. The only reason is_error_noslot_pfn() was
> checked instead is because we did not have the slot before
> commit 6574422f913e ("KVM: x86/mmu: Pass the memslot around via struct
> kvm_page_fault") and looking up the memslot is expensive.
> 
> Now that the slot is available, explicitly check if it's null and
> get rid of the redundant is_error_noslot_pfn() check.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

Re: [PATCH] KVM: x86/mmu: Refactor slot null check in kvm_mmu_hugepage_adjust

[Paolo Bonzini]

On 25/08/21 01:34, David Matlack wrote:
> The current code is correct but relies on is_error_noslot_pfn() to
> ensure slot is not null. The only reason is_error_noslot_pfn() was
> checked instead is because we did not have the slot before
> commit 6574422f913e ("KVM: x86/mmu: Pass the memslot around via struct
> kvm_page_fault") and looking up the memslot is expensive.
> 
> Now that the slot is available, explicitly check if it's null and
> get rid of the redundant is_error_noslot_pfn() check.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>   arch/x86/kvm/mmu/mmu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4853c033e6ce..9b5424bcb173 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2925,10 +2925,10 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>   	if (unlikely(fault->max_level == PG_LEVEL_4K))
>   		return;
>   
> -	if (is_error_noslot_pfn(fault->pfn) || kvm_is_reserved_pfn(fault->pfn))
> +	if (!slot || kvm_slot_dirty_track_enabled(slot))
>   		return;
>   
> -	if (kvm_slot_dirty_track_enabled(slot))
> +	if (kvm_is_reserved_pfn(fault->pfn))
>   		return;
>   
>   	/*
> 

Squashed, thanks.

Paolo