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    Subject[PATCH 28/35] KVM: MMU: Set the accessed bit on non-speculative shadow ptes
    Date
    If we populate a shadow pte due to a fault (and not speculatively due to a
    pte write) then we can set the accessed bit on it, as we know it will be
    set immediately on the next guest instruction. This saves a read-modify-write
    operation.

    Signed-off-by: Avi Kivity <avi@qumranet.com>
    ---
    arch/x86/kvm/mmu.c | 8 +++++---
    arch/x86/kvm/paging_tmpl.h | 4 ++--
    2 files changed, 7 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index 072e942..a5872b3 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -1020,7 +1020,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
    unsigned pt_access, unsigned pte_access,
    int user_fault, int write_fault, int dirty,
    int *ptwrite, int largepage, gfn_t gfn,
    - struct page *page)
    + struct page *page, bool speculative)
    {
    u64 spte;
    int was_rmapped = 0;
    @@ -1061,6 +1061,8 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
    * demand paging).
    */
    spte = PT_PRESENT_MASK | PT_DIRTY_MASK;
    + if (!speculative)
    + pte_access |= PT_ACCESSED_MASK;
    if (!dirty)
    pte_access &= ~ACC_WRITE_MASK;
    if (!(pte_access & ACC_EXEC_MASK))
    @@ -1148,13 +1150,13 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,

    if (level == 1) {
    mmu_set_spte(vcpu, &table[index], ACC_ALL, ACC_ALL,
    - 0, write, 1, &pt_write, 0, gfn, page);
    + 0, write, 1, &pt_write, 0, gfn, page, false);
    return pt_write;
    }

    if (largepage && level == 2) {
    mmu_set_spte(vcpu, &table[index], ACC_ALL, ACC_ALL,
    - 0, write, 1, &pt_write, 1, gfn, page);
    + 0, write, 1, &pt_write, 1, gfn, page, false);
    return pt_write;
    }

    diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
    index 57abbd0..e9ae5db 100644
    --- a/arch/x86/kvm/paging_tmpl.h
    +++ b/arch/x86/kvm/paging_tmpl.h
    @@ -266,7 +266,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
    get_page(npage);
    mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
    gpte & PT_DIRTY_MASK, NULL, largepage, gpte_to_gfn(gpte),
    - npage);
    + npage, true);
    }

    /*
    @@ -349,7 +349,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
    mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
    user_fault, write_fault,
    walker->ptes[walker->level-1] & PT_DIRTY_MASK,
    - ptwrite, largepage, walker->gfn, page);
    + ptwrite, largepage, walker->gfn, page, false);

    return shadow_ent;
    }
    --
    1.5.4.5


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