Groups > linux.kernel > #1719050

Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU
Date	2017-08-24 11:20 +0200
Message-ID	<uhWsW-4xQ-23@gated-at.bofh.it> (permalink)
References	<uhLnP-5N6-5@gated-at.bofh.it> <uhLnP-5N6-3@gated-at.bofh.it> <uhWjg-4uA-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 24/08/2017 11:09, Yang Zhang wrote:
>> +    if (static_cpu_has(X86_FEATURE_OSPKE) &&
> 
> We expose protection key to VM without check whether OSPKE is enabled or
> not. Why not check guest's cpuid here which also can avoid unnecessary
> access to pkru?

Checking guest CPUID is pretty slow.  We could check CR4.PKE though.

Also, using static_cpu_has with OSPKE is probably wrong.  But if we do
check CR4.PKE, we can check X86_FEATURE_PKU instead, so something like

	if (static_cpu_has(X86_FEATURE_PKU) &&
	    kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
	    vcpu->arch.pkru != vmx->host_pkru)

... but then, kvm_read_cr4_bits is also pretty slow---and we don't
really need it, since all CR4 writes cause a vmexit.  So for now I'd
stay with this patch, only s/static_cpu_has/boot_cpu_has/g.

Of course you can send improvements on top!

Paolo

>> +        vcpu->arch.pkru != vmx->host_pkru)
>> +        __write_pkru(vcpu->arch.pkru);

Thread

[PATCH 1/2] KVM: x86: simplify handling of PKRU Paolo Bonzini <pbonzini@redhat.com> - 2017-08-23 23:30 +0200
  Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-24 11:10 +0200
    Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU Paolo Bonzini <pbonzini@redhat.com> - 2017-08-24 11:20 +0200
      Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU Yang Zhang <yang.zhang.wz@gmail.com> - 2017-08-24 12:10 +0200
        Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU Paolo Bonzini <pbonzini@redhat.com> - 2017-08-24 12:20 +0200

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