2022-12-21 22:27:52

by Ben Gardon

Subject: [RFC 09/14] KVM: x86/MMU: Only make pages available on Shadow MMU fault

Now that the Shadow MMU has been factored out of mmu.c and the naming
sheme has been cleaned up, it's clear that there's an unnecessary
operation in direct_page_fault(). Since the MMU page quota is only
applied to the Shadow MMU, there's no point to calling
kvm_shadow_mmu_make_pages_available on a fault where the TDP MMU is
going to handle installing new TDP PTEs.

Signed-off-by: Ben Gardon <[email protected]>
---
arch/x86/kvm/mmu/mmu.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index bacb519ba7b4..568b36de9eeb 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1469,14 +1469,14 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
if (is_page_fault_stale(vcpu, fault, mmu_seq))
goto out_unlock;

- r = kvm_shadow_mmu_make_pages_available(vcpu);
- if (r)
- goto out_unlock;
-
if (is_tdp_mmu_fault)
r = kvm_tdp_mmu_map(vcpu, fault);
- else
+ else {
+ r = kvm_shadow_mmu_make_pages_available(vcpu);
+ if (r)
+ goto out_unlock;
r = kvm_shadow_mmu_direct_map(vcpu, fault);
+ }

out_unlock:
if (is_tdp_mmu_fault)
--
2.39.0.314.g84b9a713c41-goog

2022-12-29 18:38:20

by David Matlack

Subject: Re: [RFC 09/14] KVM: x86/MMU: Only make pages available on Shadow MMU fault

On Wed, Dec 21, 2022 at 2:24 PM Ben Gardon <[email protected]> wrote:
>
> Now that the Shadow MMU has been factored out of mmu.c and the naming
> sheme has been cleaned up, it's clear that there's an unnecessary
> operation in direct_page_fault(). Since the MMU page quota is only
> applied to the Shadow MMU, there's no point to calling
> kvm_shadow_mmu_make_pages_available on a fault where the TDP MMU is
> going to handle installing new TDP PTEs.

Jinx! An equivalent change recently went into kvm/queue:

https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?h=queue&id=1290f90e77186bf8a06a3a35ebf254f5b004676b