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    Subject[PATCH v2 10/16] KVM: MMU: fask check whether page is writable
    Using bit 1 (PTE_LIST_WP_BIT) in rmap store the write-protect status
    to avoid unnecessary shadow page walking

    Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
    ---
    arch/x86/kvm/mmu.c | 40 ++++++++++++++++++++++++++++++++++------
    1 files changed, 34 insertions(+), 6 deletions(-)
    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index 0c6e92d..8b71908 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -796,7 +796,9 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn)
    return level - 1;
    }

    -#define PTE_LIST_DESC (0x1ull)
    +#define PTE_LIST_DESC_BIT 0
    +#define PTE_LIST_WP_BIT 1
    +#define PTE_LIST_DESC (1 << PTE_LIST_DESC_BIT)
    #define PTE_LIST_FLAG_MASK (0x3ull)

    static void
    @@ -1067,6 +1069,12 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu)
    return mmu_memory_cache_free_objects(cache);
    }

    +static void host_page_write_protect(u64 *spte, unsigned long *rmapp)
    +{
    + if (!(*spte & SPTE_HOST_WRITEABLE))
    + __test_and_set_bit(PTE_LIST_WP_BIT, rmapp);
    +}
    +
    static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
    {
    struct kvm_mmu_page *sp;
    @@ -1074,7 +1082,10 @@ static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)

    sp = page_header(__pa(spte));
    kvm_mmu_page_set_gfn(sp, spte - sp->spt, gfn);
    +
    rmapp = gfn_to_rmap(vcpu->kvm, gfn, sp->role.level);
    + host_page_write_protect(spte, rmapp);
    +
    return pte_list_add(vcpu, spte, rmapp);
    }

    @@ -1164,16 +1175,23 @@ static bool rmap_write_protect(struct kvm *kvm, u64 gfn)
    {
    struct kvm_memory_slot *slot;
    unsigned long *rmapp;
    - int i;
    + int i = PT_PAGE_TABLE_LEVEL;
    bool write_protected = false;

    slot = gfn_to_memslot(kvm, gfn);
    + rmapp = __gfn_to_rmap(gfn, i, slot);
    +
    + if (__test_and_set_bit(PTE_LIST_WP_BIT, rmapp))
    + return false;
    +
    + do {
    + write_protected |= __rmap_write_protect(kvm, rmapp, i++);
    +
    + if (i >= PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES)
    + break;

    - for (i = PT_PAGE_TABLE_LEVEL;
    - i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {
    rmapp = __gfn_to_rmap(gfn, i, slot);
    - write_protected |= __rmap_write_protect(kvm, rmapp, i);
    - }
    + } while (true);

    return write_protected;
    }
    @@ -1225,6 +1243,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,

    mmu_spte_clear_track_bits(sptep);
    mmu_spte_set(sptep, new_spte);
    + host_page_write_protect(sptep, rmapp);
    }
    }

    @@ -2291,9 +2310,15 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
    {
    struct kvm_mmu_page *s;
    struct hlist_node *node;
    + unsigned long *rmap;
    bool need_unsync = false;

    + rmap = gfn_to_rmap(vcpu->kvm, gfn, PT_PAGE_TABLE_LEVEL);
    +
    if (!vcpu->kvm->arch.indirect_shadow_pages)
    + goto write_free;
    +
    + if (!test_bit(PTE_LIST_WP_BIT, rmap))
    return 0;

    for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn, node) {
    @@ -2309,6 +2334,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
    }
    if (need_unsync)
    kvm_unsync_pages(vcpu, gfn);
    +
    +write_free:
    + __clear_bit(PTE_LIST_WP_BIT, rmap);
    return 0;
    }

    --
    1.7.7.6


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