On Mon, 2018-10-22 at 14:42 -0700, Jim Mattson wrote:
> On Sat, Oct 20, 2018 at 3:22 PM, KarimAllah Ahmed <karah...@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 <karah...@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?
With the current implementation of the API, yes. The performance will be
horrible. This does not affect the current users though (i.e. when guest memory
is backed by "struct page").
I have a few patches that implements a pfn_cache on top of this as suggested by
Paolo. This would allow this API to be used for this type of high-frequency
mappings.
For example with this pfn_cache, booting an Ubuntu was 10x faster (from ~ 2
minutes to 13 seconds).
>
> >
> > 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
> >
>
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