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Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support

To: Keir Fraser <keir@xxxxxxx>
Subject: Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support
From: Haitao Shan <maillists.shan@xxxxxxxxx>
Date: Thu, 28 Oct 2010 19:28:03 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Weidong Han <weidong.han@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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Thanks! I will update and send the patch out later.

Shan Haitao

2010/10/28 Keir Fraser <keir@xxxxxxx>:
> On 28/10/2010 08:52, "Haitao Shan" <maillists.shan@xxxxxxxxx> wrote:
>> Then I would prefer to write XCR0 unconditionally. Otherwise, I can
>> only refer to the approach for handling CR4 switches: reading CR4
>> first and checking whether there is a need to write actually.
>> But I don't think <a read to XCR0 plus a data comparison> can save any
>> compared with one unconditional write to XCR0.
>> Are you OK with this?
> Note that read_cr4() actually returns a cached copy of cr4, as stashed by
> write_cr4(). You should use the same trick for XCR0, and then do the
> cached-read-and-compare on context switch, again just as we do for cr4.
>  -- Keir
>> Thanks for pointing out the memory leak when hvm_vcpu_initialize
>> fails. I will update accordingly.
>> Shan Haitao
>> 2010/10/28 Jan Beulich <JBeulich@xxxxxxxxxx>:
>>>>>> On 28.10.10 at 06:58, Haitao Shan <maillists.shan@xxxxxxxxx> wrote:
>>>> This is the updated patch#2. Thanks.
>>> Sorry, but this is worse than not checking at all: You didn't consider
>>> the idle vCPU case here, and hence you may end up having more
>>> features enabled in xcr0 for a guest than it should have.
>>> Also I only now noticed that you're leaking the xsave_area allocation
>>> in vcpu_initialize() if hvm_vcpu_initialise() fails.
>>> Jan
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