On Thu, Feb 03, 2022, David Matlack wrote:
> Commit fb58a9c345f6 ("KVM: x86/mmu: Optimize MMU page cache lookup for
> fully direct MMUs") skipped the unsync checks and write flood clearing
> for full direct MMUs. We can extend this further and skip the checks for
> all direct shadow pages. Direct shadow pages are never marked unsynced
> or have a non-zero write-flooding count.
>
> No functional change intended.
>
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> 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 296f8723f9ae..6ca38277f2ab 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2052,7 +2052,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
> int direct,
> unsigned int access)
> {
> - bool direct_mmu = vcpu->arch.mmu->direct_map;
> union kvm_mmu_page_role role;
> struct hlist_head *sp_list;
> unsigned quadrant;
> @@ -2093,7 +2092,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
> continue;
> }
>
> - if (direct_mmu)
> + /* unsync and write-flooding only apply to indirect SPs. */
> + if (sp->role.direct)
Because I spent waaaay too much time over-analyzing this... checking sp->role.direct
actually generates better code than check @direct. Because of regsiter pressure,
direct has to get shoved onto the stack and then pulled back off. Not that it
matters, at all, because this code runs exactly once...
> goto trace_get_page;
>
> if (sp->unsync) {
> --
> 2.35.0.rc2.247.g8bbb082509-goog
>
