| Message ID | 20210824075524.3354-8-jiangshanlai@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/7] KVM: X86: Fix missed remote tlb flush in rmap_write_protect() | expand |
On Tue, Aug 24, 2021, Lai Jiangshan wrote: > From: Lai Jiangshan <laijs@linux.alibaba.com> > > __direct_pte_prefetch() skips prefetching the last range. > > The last range are often the whole range after the faulted spte when > guest is touching huge-page-mapped(in guest view) memory forwardly > which means prefetching them can reduce pagefault. > > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> > --- > arch/x86/kvm/mmu/mmu.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index e5932af6f11c..ac260e01e9d8 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -2847,8 +2847,9 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu, > i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1); > spte = sp->spt + i; > > - for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) { > - if (is_shadow_present_pte(*spte) || spte == sptep) { > + for (i = 0; i <= PTE_PREFETCH_NUM; i++, spte++) { > + if (i == PTE_PREFETCH_NUM || > + is_shadow_present_pte(*spte) || spte == sptep) { Heh, I posted a fix just a few days ago. I prefer having a separate call after the loop. The "<= PTE_PREFETCH_NUM" is subtle, and a check at the ends avoids a CMP+Jcc in the loop, though I highly doubt that actually affects performance. https://lkml.kernel.org/r/20210818235615.2047588-1-seanjc@google.com > if (!start) > continue; > if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0) > -- > 2.19.1.6.gb485710b >
On Wed, Aug 25, 2021 at 11:18 PM Sean Christopherson <seanjc@google.com> wrote: > > On Tue, Aug 24, 2021, Lai Jiangshan wrote: > > From: Lai Jiangshan <laijs@linux.alibaba.com> > > > > __direct_pte_prefetch() skips prefetching the last range. > > > > The last range are often the whole range after the faulted spte when > > guest is touching huge-page-mapped(in guest view) memory forwardly > > which means prefetching them can reduce pagefault. > > > > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> > > --- > > arch/x86/kvm/mmu/mmu.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index e5932af6f11c..ac260e01e9d8 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -2847,8 +2847,9 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu, > > i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1); > > spte = sp->spt + i; > > > > - for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) { > > - if (is_shadow_present_pte(*spte) || spte == sptep) { > > + for (i = 0; i <= PTE_PREFETCH_NUM; i++, spte++) { > > + if (i == PTE_PREFETCH_NUM || > > + is_shadow_present_pte(*spte) || spte == sptep) { > > Heh, I posted a fix just a few days ago. I prefer having a separate call after > the loop. The "<= PTE_PREFETCH_NUM" is subtle, and a check at the ends avoids > a CMP+Jcc in the loop, though I highly doubt that actually affects performance. > > https://lkml.kernel.org/r/20210818235615.2047588-1-seanjc@google.com Thanks! > > > if (!start) > > continue; > > if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0) > > -- > > 2.19.1.6.gb485710b > >
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index e5932af6f11c..ac260e01e9d8 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2847,8 +2847,9 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu, i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1); spte = sp->spt + i; - for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) { - if (is_shadow_present_pte(*spte) || spte == sptep) { + for (i = 0; i <= PTE_PREFETCH_NUM; i++, spte++) { + if (i == PTE_PREFETCH_NUM || + is_shadow_present_pte(*spte) || spte == sptep) { if (!start) continue; if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0)