Re: [PATCH v3 06/13] KVM/nVMX: Use kvm_vcpu_map when mapping the L1 MSR bitmap

Jim Mattson
2018-10-22T21:42:35Z

On Sat, Oct 20, 2018 at 3:22 PM, KarimAllah Ahmed <karahmed@amazon.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@amazon.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
>