linux-kernel - Re: [PATCH v3 06/13] KVM/nVMX: Use kvm_vcpu

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Date:   Mon, 22 Oct 2018 14:42:35 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v3 06/13] KVM/nVMX: Use kvm_vcpu_map when mapping the L1
 MSR bitmap

On Sat, Oct 20, 2018 at 3:22 PM, KarimAllah Ahmed <karahmed@...zon.de> wrote:
> Use kvm_vcpu_map when mapping the L1 MSR bitmap since using
> kvm_vcpu_gpa_to_page() and kmap() will only work for guest memory that has
> a "struct page".
>
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
> v1 -> v2:
> - Do not change the lifecycle of the mapping (pbonzini)
> ---
>  arch/x86/kvm/vmx.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d857401..5b15ca2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -847,6 +847,9 @@ struct nested_vmx {
>         struct page *apic_access_page;
>         struct page *virtual_apic_page;
>         struct page *pi_desc_page;
> +
> +       struct kvm_host_map msr_bitmap_map;
> +
>         struct pi_desc *pi_desc;
>         bool pi_pending;
>         u16 posted_intr_nv;
> @@ -11546,9 +11549,10 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
>                                                  struct vmcs12 *vmcs12)
>  {
>         int msr;
> -       struct page *page;
>         unsigned long *msr_bitmap_l1;
>         unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.vmcs02.msr_bitmap;
> +       struct kvm_host_map *map = &to_vmx(vcpu)->nested.msr_bitmap_map;
> +
>         /*
>          * pred_cmd & spec_ctrl are trying to verify two things:
>          *
> @@ -11574,11 +11578,10 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
>             !pred_cmd && !spec_ctrl)
>                 return false;
>
> -       page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->msr_bitmap);
> -       if (is_error_page(page))
> +       if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), map))

Isn't this the sort of high frequency operation that should not use the new API?

>                 return false;
>
> -       msr_bitmap_l1 = (unsigned long *)kmap(page);
> +       msr_bitmap_l1 = (unsigned long *)map->hva;
>         if (nested_cpu_has_apic_reg_virt(vmcs12)) {
>                 /*
>                  * L0 need not intercept reads for MSRs between 0x800 and 0x8ff, it
> @@ -11626,8 +11629,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
>                                         MSR_IA32_PRED_CMD,
>                                         MSR_TYPE_W);
>
> -       kunmap(page);
> -       kvm_release_page_clean(page);
> +       kvm_vcpu_unmap(&to_vmx(vcpu)->nested.msr_bitmap_map);
>
>         return true;
>  }
> --
> 2.7.4
>