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    Subject[PATCH 7/9] x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept_mmu
    Date
    MMU re-initialization is expensive, in particular,
    update_permission_bitmask() and update_pkru_bitmask() are.

    Cache the data used to setup shadow EPT MMU and avoid full re-init when
    it is unchanged.

    Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    ---
    arch/x86/include/asm/kvm_host.h | 14 +++++++++++
    arch/x86/kvm/mmu.c | 51 ++++++++++++++++++++++++++++++-----------
    2 files changed, 52 insertions(+), 13 deletions(-)

    diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
    index 830166ab4d59..d44668dcf655 100644
    --- a/arch/x86/include/asm/kvm_host.h
    +++ b/arch/x86/include/asm/kvm_host.h
    @@ -272,8 +272,22 @@ union kvm_mmu_page_role {
    };
    };

    +/*
    + * This structure complements kvm_mmu_page_role caching everything needed for
    + * MMU configuration. If nothing in both these structures changed, MMU
    + * re-configuration can be skipped. @valid bit is set on first usage so we don't
    + * treat all-zero structure as valid data.
    + */
    union kvm_mmu_scache {
    unsigned int word;
    + struct {
    + unsigned int valid:1;
    + unsigned int execonly:1;
    + unsigned int cr4_pse:1;
    + unsigned int cr4_pke:1;
    + unsigned int cr4_smap:1;
    + unsigned int cr4_smep:1;
    + };
    };

    union kvm_mmu_role {
    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index c538e47e471b..c46f875bf937 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -4678,6 +4678,24 @@ static void paging32E_init_context(struct kvm_vcpu *vcpu,
    paging64_init_context_common(vcpu, context, PT32E_ROOT_LEVEL);
    }

    +static union kvm_mmu_role
    +kvm_calc_mmu_role_common(struct kvm_vcpu *vcpu)
    +{
    + union kvm_mmu_role role = {0};
    +
    + role.base_role.access = ACC_ALL;
    + role.base_role.cr0_wp = is_write_protection(vcpu);
    +
    + role.scache.cr4_smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP) != 0;
    + role.scache.cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP) != 0;
    + role.scache.cr4_pse = !!is_pse(vcpu);
    + role.scache.cr4_pke = kvm_read_cr4_bits(vcpu, X86_CR4_PKE) != 0;
    +
    + role.scache.valid = 1;
    +
    + return role;
    +}
    +
    static union kvm_mmu_page_role
    kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu)
    {
    @@ -4784,16 +4802,18 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
    }
    EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);

    -static union kvm_mmu_page_role
    -kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty)
    +static union kvm_mmu_role
    +kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty,
    + bool execonly)
    {
    - union kvm_mmu_page_role role = vcpu->arch.mmu->mmu_role.base_role;
    + union kvm_mmu_role role = kvm_calc_mmu_role_common(vcpu);

    - role.level = PT64_ROOT_4LEVEL;
    - role.direct = false;
    - role.ad_disabled = !accessed_dirty;
    - role.guest_mode = true;
    - role.access = ACC_ALL;
    + role.base_role.level = PT64_ROOT_4LEVEL;
    + role.base_role.direct = false;
    + role.base_role.ad_disabled = !accessed_dirty;
    + role.base_role.guest_mode = true;
    +
    + role.scache.execonly = execonly;

    return role;
    }
    @@ -4802,10 +4822,16 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
    bool accessed_dirty, gpa_t new_eptp)
    {
    struct kvm_mmu *context = vcpu->arch.mmu;
    - union kvm_mmu_page_role root_page_role =
    - kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty);
    + union kvm_mmu_role new_role =
    + kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
    + execonly);
    +
    + __kvm_mmu_new_cr3(vcpu, new_eptp, new_role.base_role, false);
    +
    + new_role.base_role.word &= mmu_base_role_mask.word;
    + if (new_role.as_u64 == context->mmu_role.as_u64)
    + return;

    - __kvm_mmu_new_cr3(vcpu, new_eptp, root_page_role, false);
    context->shadow_root_level = PT64_ROOT_4LEVEL;

    context->nx = true;
    @@ -4817,8 +4843,7 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
    context->update_pte = ept_update_pte;
    context->root_level = PT64_ROOT_4LEVEL;
    context->direct_map = false;
    - context->mmu_role.base_role.word =
    - root_page_role.word & mmu_base_role_mask.word;
    + context->mmu_role.as_u64 = new_role.as_u64;
    context->get_pdptr = kvm_pdptr_read;

    update_permission_bitmask(vcpu, context, true);
    --
    2.14.4
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