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SubjectRe: [RFC 2/7] KVM: VMX: Expose IA32_PKRS MSR
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On 07/08/20 10:48, Chenyi Qiang wrote:
> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
> + bool pks_supported = guest_cpuid_has(vcpu, X86_FEATURE_PKS);
> +
> + /*
> + * set intercept for PKRS when the guest doesn't support pks
> + */
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PKRS, MSR_TYPE_RW, !pks_supported);
> +
> + if (pks_supported) {
> + vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_PKRS);
> + vm_exit_controls_setbit(vmx, VM_EXIT_LOAD_IA32_PKRS);
> + } else {
> + vm_entry_controls_clearbit(vmx, VM_ENTRY_LOAD_IA32_PKRS);
> + vm_exit_controls_clearbit(vmx, VM_EXIT_LOAD_IA32_PKRS);
> + }

Is the guest expected to do a lot of reads/writes to the MSR (e.g. at
every context switch)?

Even if this is the case, the MSR intercepts and the entry/exit controls
should only be done if CR4.PKS=1. If the guest does not use PKS, KVM
should behave as if these patches did not exist.

Paolo

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