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SubjectRe: [PATCH v8 6/8] KVM: x86: VMX: Prevent MSR passthrough when MSR access is denied
Hi,

I reported in the v13 cover letter of kvm dirty ring series that this patch
seems to have been broken. Today I tried to reproduce with a simplest vm, and
after a closer look...

On Fri, Sep 25, 2020 at 04:34:20PM +0200, Alexander Graf wrote:
> @@ -3764,15 +3859,14 @@ static u8 vmx_msr_bitmap_mode(struct kvm_vcpu *vcpu)
> return mode;
> }
>
> -static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu,
> - unsigned long *msr_bitmap, u8 mode)
> +static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu, u8 mode)
> {
> int msr;
>
> - for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
> - unsigned word = msr / BITS_PER_LONG;
> - msr_bitmap[word] = (mode & MSR_BITMAP_MODE_X2APIC_APICV) ? 0 : ~0;
> - msr_bitmap[word + (0x800 / sizeof(long))] = ~0;
> + for (msr = 0x800; msr <= 0x8ff; msr++) {
> + bool intercepted = !!(mode & MSR_BITMAP_MODE_X2APIC_APICV);
> +
> + vmx_set_intercept_for_msr(vcpu, msr, MSR_TYPE_RW, intercepted);
> }
>
> if (mode & MSR_BITMAP_MODE_X2APIC) {

... I think we may want below change to be squashed:

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d160aad59697..7d3f2815b04d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3781,9 +3781,10 @@ static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu, u8 mode)
int msr;

for (msr = 0x800; msr <= 0x8ff; msr++) {
- bool intercepted = !!(mode & MSR_BITMAP_MODE_X2APIC_APICV);
+ bool apicv = mode & MSR_BITMAP_MODE_X2APIC_APICV;

- vmx_set_intercept_for_msr(vcpu, msr, MSR_TYPE_RW, intercepted);
+ vmx_set_intercept_for_msr(vcpu, msr, MSR_TYPE_R, !apicv);
+ vmx_set_intercept_for_msr(vcpu, msr, MSR_TYPE_W, true);
}

if (mode & MSR_BITMAP_MODE_X2APIC) {
This fixes my problem the same as having this patch reverted.

--
Peter Xu

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