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Date: Thu, 12 Nov 2020 11:11:43 +0100
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 01/11] KVM: x86: Get active PCID only when writing a
CR3 value
Sean Christopherson <sean.j.christopherson@...el.com> writes:
> Retrieve the active PCID only when writing a guest CR3 value, i.e. don't
> get the PCID when using EPT. The PCID is not used when EPT is enabled,
> and must be manually stripped, which is annoying and unnecessary.
> And on VMX, getting the active PCID also involves reading the guest's
> CR3 and CR4.PCIDE, i.e. may add pointless VMREADs.
>
> Opportunistically rename the pgd/pgd_level params to root_hpa and
> root_level to better reflect their new roles. Keep the function names,
> as "load the guest PGD" is still accurate/correct.
>
> Last, and probably least, pass root_hpa as a hpa_t/u64 instead of an
> unsigned long. The EPTP holds a 64-bit value, even in 32-bit mode, so
> in theory EPT could support HIGHMEM for 32-bit KVM. Never mind that
> doing so would require changing the MMU page allocators and reworking
> the MMU to use kmap().
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
> arch/x86/include/asm/kvm_host.h | 4 ++--
> arch/x86/kvm/mmu.h | 2 +-
> arch/x86/kvm/svm/svm.c | 4 ++--
> arch/x86/kvm/vmx/vmx.c | 13 ++++++-------
> arch/x86/kvm/vmx/vmx.h | 3 +--
> 5 files changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d44858b69353..33b2acfd7869 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1181,8 +1181,8 @@ struct kvm_x86_ops {
> int (*set_identity_map_addr)(struct kvm *kvm, u64 ident_addr);
> u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
>
> - void (*load_mmu_pgd)(struct kvm_vcpu *vcpu, unsigned long pgd,
> - int pgd_level);
> + void (*load_mmu_pgd)(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> + int root_level);
>
> bool (*has_wbinvd_exit)(void);
>
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 9c4a9c8e43d9..add537a39177 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -95,7 +95,7 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
> if (!VALID_PAGE(root_hpa))
> return;
>
> - kvm_x86_ops.load_mmu_pgd(vcpu, root_hpa | kvm_get_active_pcid(vcpu),
> + kvm_x86_ops.load_mmu_pgd(vcpu, root_hpa,
> vcpu->arch.mmu->shadow_root_level);
> }
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index cf951e588dd1..4a6a5a3dc963 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3667,13 +3667,13 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
> return svm_exit_handlers_fastpath(vcpu);
> }
>
> -static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long root,
> +static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> int root_level)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> unsigned long cr3;
>
> - cr3 = __sme_set(root);
> + cr3 = __sme_set(root_hpa) | kvm_get_active_pcid(vcpu);
> if (npt_enabled) {
> svm->vmcb->control.nested_cr3 = cr3;
> vmcb_mark_dirty(svm->vmcb, VMCB_NPT);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 281c405c7ea3..273a3206cef7 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3043,8 +3043,7 @@ static int vmx_get_max_tdp_level(void)
> return 4;
> }
>
> -u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa,
> - int root_level)
> +u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level)
> {
> u64 eptp = VMX_EPTP_MT_WB;
>
> @@ -3053,13 +3052,13 @@ u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa,
> if (enable_ept_ad_bits &&
> (!is_guest_mode(vcpu) || nested_ept_ad_enabled(vcpu)))
> eptp |= VMX_EPTP_AD_ENABLE_BIT;
> - eptp |= (root_hpa & PAGE_MASK);
> + eptp |= root_hpa;
(Nitpicking according to personal taste):
It looks a bit weird that we start building 'eptp' from flags and add
pointer as the last step, I'd suggest we re-write the function as:
u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level)
{
u64 eptp = root_hpa | VMX_EPTP_MT_WB;
eptp |= (root_level == 5) ? VMX_EPTP_PWL_5 : VMX_EPTP_PWL_4;
if (enable_ept_ad_bits &&
(!is_guest_mode(vcpu) || nested_ept_ad_enabled(vcpu)))
eptp |= VMX_EPTP_AD_ENABLE_BIT;
return eptp;
}
>
> return eptp;
> }
>
> -static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
> - int pgd_level)
> +static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> + int root_level)
> {
> struct kvm *kvm = vcpu->kvm;
> bool update_guest_cr3 = true;
> @@ -3067,7 +3066,7 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
> u64 eptp;
>
> if (enable_ept) {
> - eptp = construct_eptp(vcpu, pgd, pgd_level);
> + eptp = construct_eptp(vcpu, root_hpa, root_level);
> vmcs_write64(EPT_POINTER, eptp);
>
> if (kvm_x86_ops.tlb_remote_flush) {
> @@ -3086,7 +3085,7 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
> update_guest_cr3 = false;
> vmx_ept_load_pdptrs(vcpu);
> } else {
> - guest_cr3 = pgd;
> + guest_cr3 = root_hpa | kvm_get_active_pcid(vcpu);
> }
>
> if (update_guest_cr3)
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index f6f66e5c6510..a2d143276603 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -326,8 +326,7 @@ void set_cr4_guest_host_mask(struct vcpu_vmx *vmx);
> void ept_save_pdptrs(struct kvm_vcpu *vcpu);
> void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
> void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
> -u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa,
> - int root_level);
> +u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
>
> void update_exception_bitmap(struct kvm_vcpu *vcpu);
> void vmx_update_msr_bitmap(struct kvm_vcpu *vcpu);
Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
--
Vitaly
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