Re: [PATCH v4 6/6] KVM: VMX: Make CR0.WP a guest owned bit

Sean Christopherson
2023-03-30T20:36:57Z

On Thu, Mar 30, 2023, Mathias Krause wrote:
> On 30.03.23 22:15, Mathias Krause wrote:
> > [...]
> > Maybe it's not a stale CR0 value but the page table walker not taking
> > the guest's CR0.WP into account? Maybe a missing role update?
>
> Indeed, it is. This does the trick for me:
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 31be188aa842..6a9e90725c84 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8372,6 +8372,9 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
>
> init_decode_cache(ctxt);
> vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
> + /* Ensure we're doing page table walks with an up2date MMU role */
> + if ((vcpu->arch.cr0 ^ kvm_read_cr0(vcpu)) == X86_CR0_WP)
> + kvm_init_mmu(vcpu);
> }
>
> void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip)
>
> Very heavy weight and misplaced, but a start :)
>
> It should (1) be limited to VMX as that's the only one that would make
> CR0.WP a guest owned bit and (2) limited to emulated instructions that
> actually do write operations, as read are harmless, obviously.

For the record, I wrote my email before I saw this ;-)