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    Subject[PATCH 5/5] KVM: x86: MMU: Eliminate an extra memory slot search in mapping_level()
    Calling kvm_vcpu_gfn_to_memslot() twice in mapping_level() should be
    avoided since getting a slot by binary search may not be negligible,
    especially for virtual machines with many memory slots.

    Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
    ---
    arch/x86/kvm/mmu.c | 17 +++++++++++------
    1 file changed, 11 insertions(+), 6 deletions(-)

    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index 78a3d08..8d285dc 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -818,14 +818,11 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
    kvm->arch.indirect_shadow_pages--;
    }

    -static int has_wrprotected_page(struct kvm_vcpu *vcpu,
    - gfn_t gfn,
    - int level)
    +static int __has_wrprotected_page(gfn_t gfn, int level,
    + struct kvm_memory_slot *slot)
    {
    - struct kvm_memory_slot *slot;
    struct kvm_lpage_info *linfo;

    - slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
    if (slot) {
    linfo = lpage_info_slot(gfn, slot, level);
    return linfo->write_count;
    @@ -834,6 +831,14 @@ static int has_wrprotected_page(struct kvm_vcpu *vcpu,
    return 1;
    }

    +static int has_wrprotected_page(struct kvm_vcpu *vcpu, gfn_t gfn, int level)
    +{
    + struct kvm_memory_slot *slot;
    +
    + slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
    + return __has_wrprotected_page(gfn, level, slot);
    +}
    +
    static int host_mapping_level(struct kvm *kvm, gfn_t gfn)
    {
    unsigned long page_size;
    @@ -893,7 +898,7 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
    max_level = min(kvm_x86_ops->get_lpage_level(), host_level);

    for (level = PT_DIRECTORY_LEVEL; level <= max_level; ++level)
    - if (has_wrprotected_page(vcpu, large_gfn, level))
    + if (__has_wrprotected_page(large_gfn, level, slot))
    break;

    return level - 1;
    --
    1.7.9.5


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