linux-kernel - Re: [PATCH] KVM: x86: do not save guest-unsupported XSAVE state

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Date:   Wed, 1 Feb 2017 16:13:36 -0800
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: do not save guest-unsupported XSAVE state



On 01/02/2017 05:19, Radim Krčmář wrote:
> Saving unsupported state prevents migration when the new host does not
> support a XSAVE feature of the original host, even if the feature is not
> exposed to the guest.
> 
> We've masked host features with guest-visible features before, with
> 4344ee981e21 ("KVM: x86: only copy XSAVE state for the supported
> features") and dropped it when implementing XSAVES.  Do it again.
> 
> Fixes: df1daba7d1cb ("KVM: x86: support XSAVES usage in the host")
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>

Cc: stable@...r.kernel.org
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

Please apply to kvm/master and send it yourself to Linus since I don't
have access to my machine this week.

Paolo

> ---
>  arch/x86/kvm/x86.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 96dd7dd13ee6..5f013ad89b57 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3221,6 +3221,7 @@ static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
>  	memcpy(dest, xsave, XSAVE_HDR_OFFSET);
>  
>  	/* Set XSTATE_BV */
> +	xstate_bv &= vcpu->arch.guest_supported_xcr0 | XFEATURE_MASK_FPSSE;
>  	*(u64 *)(dest + XSAVE_HDR_OFFSET) = xstate_bv;
>  
>  	/*
>