linux-kernel - Re: [PATCH] kvm/svm: PKU not currently supported

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Message-ID: <87immc873u.fsf@vitty.brq.redhat.com>
Date:   Thu, 19 Dec 2019 20:09:57 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     John Allen <john.allen@....com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        rkrcmar@...hat.com, John Allen <john.allen@....com>
Subject: Re: [PATCH] kvm/svm: PKU not currently supported

John Allen <john.allen@....com> writes:

> Current SVM implementation does not have support for handling PKU. Guests
> running on a host with future AMD cpus that support the feature will read
> garbage from the PKRU register and will hit segmentation faults on boot as
> memory is getting marked as protected that should not be. Ensure that cpuid
> from SVM does not advertise the feature.
>
> Signed-off-by: John Allen <john.allen@....com>
> ---
>  arch/x86/kvm/svm.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 122d4ce3b1ab..f911aa1b41c8 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5933,6 +5933,8 @@ static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
>  		if (avic)
>  			entry->ecx &= ~bit(X86_FEATURE_X2APIC);
>  		break;
> +	case 0x7:
> +		entry->ecx &= ~bit(X86_FEATURE_PKU);

Would it make more sense to introduce kvm_x86_ops->pku_supported() (and
return false for SVM and boot_cpu_has(X86_FEATURE_PKU) for vmx) so we
don't set the bit in the first place?

>  	case 0x80000001:
>  		if (nested)
>  			entry->ecx |= (1 << 2); /* Set SVM bit */

-- 
Vitaly