Re: [PATCH v2 3/3] KVM: VMX: make MSR bitmaps per-VCPU

From: Radim KrÄmÃÅ
Date: Tue Jan 30 2018 - 11:24:19 EST


2018-01-27 09:50+0100, Paolo Bonzini:
> Place the MSR bitmap in struct loaded_vmcs, and update it in place
> every time the x2apic or APICv state can change. This is rare and
> the loop can handle 64 MSRs per iteration, in a similar fashion as
> nested_vmx_prepare_msr_bitmap.
>
> This prepares for choosing, on a per-VM basis, whether to intercept
> the SPEC_CTRL and PRED_CMD MSRs.
>
> Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> @@ -10022,7 +10043,7 @@ static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
> int msr;
> struct page *page;
> unsigned long *msr_bitmap_l1;
> - unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.msr_bitmap;
> + unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.vmcs02.msr_bitmap;

The physical address of the nested msr_bitmap is never loaded into vmcs.

The resolution you provided had extra hunk in prepare_vmcs02_full():

+ vmcs_write64(MSR_BITMAP, __pa(vmx->nested.vmcs02.msr_bitmap));

I have queued that as:

+ if (cpu_has_vmx_msr_bitmap())
+ vmcs_write64(MSR_BITMAP, __pa(vmx->nested.vmcs02.msr_bitmap));

but it should be a part of the patch or a followup fix.

Is the branch already merged into PTI?

Thanks.

>
> /* This shortcut is ok because we support only x2APIC MSRs so far. */
> if (!nested_cpu_has_virt_x2apic_mode(vmcs12))
> @@ -11397,7 +11418,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
> vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
>
> if (cpu_has_vmx_msr_bitmap())
> - vmx_set_msr_bitmap(vcpu);
> + vmx_update_msr_bitmap(vcpu);
>
> if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr,
> vmcs12->vm_exit_msr_load_count))
> --
> 1.8.3.1
>