linux-kernel - Re: [CFT PATCH v2 0/2] KVM: support XSAVES usage in the host

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Date:	Tue, 25 Nov 2014 15:17:20 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Nadav Amit <nadav.amit@...il.com>
CC:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Nadav Amit <namit@...technion.ac.il>, hpa@...ux.intel.com
Subject: Re: [CFT PATCH v2 0/2] KVM: support XSAVES usage in the host



On 25/11/2014 15:05, Nadav Amit wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 373b0ab9a32e..ca26681455c2 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -6955,6 +6955,9 @@ int fx_init(struct kvm_vcpu *vcpu)
> > 		return err;
> > 
> > 	fpu_finit(&vcpu->arch.guest_fpu);
> > +	if (cpu_has_xsaves)
> > +		vcpu->arch.guest_fpu.state->xsave.xsave_hdr.xcomp_bv =
> > +			host_xcr0 | XSTATE_COMPACTION_ENABLED;
> > 
> > 	/*
> > 	 * Ensure guest xcr0 is valid for loading
> 
> The second version works for me (w/qemu v2.1.0; Linux 3.13 guest). I
> did not need to apply this patch on top. [although I am not sure whether
> relying on userspace to call KVM_SET_XSAVE early enough is a good practice].

Did you actually try the patch? :)  If it works, I'm tempted to apply it
anyway.

> One disclaimer: Since I got limited time with the machine, I executed
> a slightly modified kernel/qemu, and not the latest version.
> Anyhow, I don’t think these differences can have any impact.

Yes, that is no problem.

Paolo
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