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

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Date:	Wed, 26 Nov 2014 11:00:34 +0200
From:	Nadav Amit <nadav.amit@...il.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, 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

Wanpeng Li <wanpeng.li@...ux.intel.com> wrote:

> 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)?
I guess this paragraph is intended for me. As I said before, I got limited
access to the machine - I will not be able to run these experiments before
Sunday, and I am not sure that I will have time to fully debug it. If you
insist, the very least please run some experiments running a 3.16 (or older)
guest kernel and running 3.17 with ‘noxsaves’ kernel parameter.

> +       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. 
xsaves is already enabled in KVM (the host) since 3.17. It just didn’t work…

Nadav

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