WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Fwd: [Xen-devel] [Patch 4/4] Refining Xsave/Xrestore support

To: xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Fwd: [Xen-devel] [Patch 4/4] Refining Xsave/Xrestore support
From: Haitao Shan <maillists.shan@xxxxxxxxx>
Date: Thu, 28 Oct 2010 10:32:39 +0800
Cc:
Delivery-date: Wed, 27 Oct 2010 19:34:23 -0700
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=cIjSbKmH39xv4FUE0OmKsQxaJ4JN7R/QwyZABPoMDk8=; b=ay2X7p84QOdwqpGEdhbhc1TbYER9nZoyN2Ot04dc8YQ024qXrE9NcSTJgL31H420al Y8b4fhfWY1Wxyn0Cd5QzyZeDIWMgXchE6gZf0FtWxN4lpM4QTkKkKGuIneZHRbDBGYvn 8joF0lbsu477JB2dloWzmjJ4MWMPsKsM7SSNI=
Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=je4gp+0j/pmF0C+VTiFNNvOoYHDCCZmWTwj9n2gwb41pvosk6CoN8SBsjgL3DNqCCl 5JEYK5d48e0h+a7XoyZ+fF9evLdmdHtVF1caSnGOoCSiMscsUdaHElqt7avA/dpbfgzM AaiBCi8nam0quqwP+XMo5DBA7H8LKihDhwk84=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <AANLkTi=1fW3rQL+8SRAzYv3D6Lqo2PGC7uYzd5VkX8hw@xxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <AANLkTi=ppSKUtJNEmpqUtCHZDqG8zfkLVKZf_1QWNhBM@xxxxxxxxxxxxxx> <20101027102530.GY4007@xxxxxxxxxxxxxxxxxxxxxxx> <AANLkTi=1fW3rQL+8SRAzYv3D6Lqo2PGC7uYzd5VkX8hw@xxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Sorry, I forget to reply to all in my reply to Deegan.

Shan Haitao


---------- Forwarded message ----------
From: Haitao Shan <maillists.shan@xxxxxxxxx>
Date: 2010/10/28
Subject: Re: [Xen-devel] [Patch 4/4] Refining Xsave/Xrestore support
To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>


Hi, Deegan,

Thanks for your review. Please see my reply embedded.

2010/10/27 Tim Deegan <Tim.Deegan@xxxxxxxxxx>:
> Hi,
>
> Thanks for this - good to see XSAVE save/restore working.  I've no
> comments on the tools part of this patch; it looks plausible but I
> haven't reviewed it closely.
>
> On the Xen HVM side:
>
>> diff -r 9bf6b4030d70 xen/arch/x86/hvm/hvm.c
>> --- a/xen/arch/x86/hvm/hvm.c  Wed Oct 27 21:55:45 2010 +0800
>> +++ b/xen/arch/x86/hvm/hvm.c  Wed Oct 27 22:17:24 2010 +0800
>> @@ -575,8 +575,13 @@ static int hvm_save_cpu_ctxt(struct doma
>>          vc = &v->arch.guest_context;
>>
>>          if ( v->fpu_initialised )
>> -            memcpy(ctxt.fpu_regs, &vc->fpu_ctxt, sizeof(ctxt.fpu_regs));
>> -        else
>> +            if ( cpu_has_xsave )
>> +                /* to restore guest img saved on xsave-incapable host */
>> +                memcpy(v->arch.xsave_area, ctxt.fpu_regs,
>> +                       sizeof(ctxt.fpu_regs));
>> +            else
>> +                memcpy(&vc->fpu_ctxt, ctxt.fpu_regs, sizeof(ctxt.fpu_regs));
>
> I think this hunk belongs in hvm_LOAD_cpu_ctxt()!
I once did the same as you said. But doing this in hvm_load_cpu_ctxt
will depends on two:
1. hvm_load_cpu_ctxt can not be executed before xsave restore routine
is executed. Otherwise, xsave_area contains no useful data at the time
of copying.
2. It seems to break restore when HVM guest (no touching eXtended
States at all) saved on a Xsave-capable host is later restored on a
Xsave-incapable host.
So I moved this part of code to hvm_save_cpu_ctxt, so that inside
guest save images FPU context is consistent.

>
>> +        else
>>              memset(ctxt.fpu_regs, 0, sizeof(ctxt.fpu_regs));
>>
>>          ctxt.rax = vc->user_regs.eax;
>
> [...]
>
>> +    ctxt = (struct hvm_hw_cpu_xsave *)&h->data[h->cur];
>> +    h->cur += desc->length;
>> +
>> +    _xfeature_mask = ctxt->xfeature_mask;
>> +    if ( (_xfeature_mask & xfeature_mask) != xfeature_mask )
>> +        return -EINVAL;
>
> This allows XSAVE records to be loaded on machines with fewer features.
> Is that safe?
Oh, my mistake I will fix that.

>
>> +    v->arch.xcr0 = ctxt->xcr0;
>> +    v->arch.xcr0_accum = ctxt->xcr0_accum;
>> +    memcpy(v->arch.xsave_area, &ctxt->save_area, xsave_cntxt_size);
>> +
>> +    return 0;
>> +}
>
> Also, have you tested this on CPUs that don't support XSAVE?  The PV
> hypercall looks like it will return -EFAULT after trying to
> copy_from_user into a null pointer on the Xen side, but something more
> explicit would be better.
Sure. I will add that in my updated patch.

>
> Cheers,
>
> Tim.
>
> --
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, XenServer Engineering
> Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)
>

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel