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

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Message-ID: <20141126012439.GA20090@kernel>
Date:	Wed, 26 Nov 2014 09:24:39 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Nadav Amit <nadav.amit@...il.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm list <kvm@...r.kernel.org>, namit@...technion.ac.il,
	hpa@...ux.intel.com
Subject: Re: [CFT PATCH v2 0/2] KVM: support XSAVES usage in the host

Hi all,
On Tue, Nov 25, 2014 at 04:50:06PM +0200, Nadav Amit wrote:
>
>> On Nov 25, 2014, at 16:17, Paolo Bonzini <pbonzini@...hat.com> wrote:
>> 
>> 
>> 
>> 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

Could you try 3.17 guest which has xsaves enabled? Because I'm not sure if 
the below codes from Paolo is enough to mask XSAVES, should we also add 
F(XSAVES)?

+       const u32 kvm_supported_word10_x86_features =
+               F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1);
+

In addition, the 3.17 guest is still hang as I mentioned even if I add the 
F(XSAVES) to the kvm_supported_word10_x86_features.

>>> 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.
>Yes, I tried it both with and without this patch.
>Due to time constraints I only tested minimal functionality (Linux boot).
>I will run more tests in the near future. Anyhow, you can put the:
>
>Tested-by: Nadav Amit <namit@...technion.ac.il>
>
>> 
>>> 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.
>
>I am just worried that Wanpeng reported it fails, while I report it works...
>

I have another patch which enable xsaves in KVM and the patch is still
under debug with Paolo's patch "KVM: x86: support XSAVES usage in the host",
so the 1/2 patch from Paolo can be dropped if my patch is ready. Anyway,
a quick fix is needed before enable xsaves in kvm. 

Regards,
Wanpeng Li 

>Nadav
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