From: Alexander Graf <agraf@suse.de>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH 2/3] kvm: svm: reset cr0 properly on vcpu reset
Date: Fri, 19 Mar 2010 16:14:44 +0100 [thread overview]
Message-ID: <4BA394E4.3080107@suse.de> (raw)
In-Reply-To: <20100319145112.GE17834@blackpad.lan.raisama.net>
Eduardo Habkost wrote:
> On Wed, Mar 17, 2010 at 10:48:23PM +0100, Alexander Graf wrote:
>
>> On 17.03.2010, at 22:42, Eduardo Habkost wrote:
>>
>>
>>> On Wed, Mar 17, 2010 at 07:17:32PM +0100, Alexander Graf wrote:
>>>
>>>> Eduardo Habkost wrote:
>>>>
>>>>> svm_vcpu_reset() was not properly resetting the contents of the guest-visible
>>>>> cr0 register, causing the following issue:
>>>>> https://bugzilla.redhat.com/show_bug.cgi?id=525699
>>>>>
>>>>> Without resetting cr0 properly, the vcpu was running the SIPI bootstrap routine
>>>>> with paging enabled, making the vcpu get a pagefault exception while trying to
>>>>> run it.
>>>>>
>>>>> Instead of setting vmcb->save.cr0 directly, the new code just resets
>>>>> kvm->arch.cr0 and calls kvm_set_cr0(). The bits that were set/cleared on
>>>>> vmcb->save.cr0 (PG, WP, !CD, !NW) will be set properly by svm_set_cr0().
>>>>>
>>>>> kvm_set_cr0() is used instead of calling svm_set_cr0() directly to make sure
>>>>> kvm_mmu_reset_context() is called to reset the mmu to nonpaging mode.
>>>>>
>>>>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>>>>>
>>>>>
>>>> Should this go into -stable?
>>>>
>>> I think so. The patch is from October, was -stable branched before that?
>>>
>> If I read the diff log correctly 2.6.32 kvm development was branched
>> off end of July 2009. The important question is if this patch fixes a
>> regression introduced by some speedup magic.
>>
>
> I have just checked git history, and it looks like this is not a
> regression. Before this patch, vcpu->cr0 (the guest-visible cr0 value)
> was never reset on vcpu reset, but only vcpu->svm->vmcb->save.cr0 (the
> actual cr0 value used by the CPU).
>
Good to know. Thanks for looking into this!
Alex
next prev parent reply other threads:[~2010-03-19 15:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-24 4:49 [PATCH 0/3] kvm: fix cr0 initialization on SIPI reset Eduardo Habkost
2009-10-24 4:49 ` [PATCH 1/3] kvm: vmx: use macros instead of hex value on cr0 initialization Eduardo Habkost
2009-10-24 4:49 ` [PATCH 2/3] kvm: svm: reset cr0 properly on vcpu reset Eduardo Habkost
2010-03-17 18:17 ` Alexander Graf
2010-03-17 21:42 ` Eduardo Habkost
2010-03-17 21:48 ` Alexander Graf
2010-03-19 14:51 ` Eduardo Habkost
2010-03-19 15:14 ` Alexander Graf [this message]
2009-10-24 4:50 ` [PATCH 3/3] kvm: svm: init_vmcb(): remove redundant save->cr0 initialization Eduardo Habkost
2009-10-25 9:40 ` [PATCH 0/3] kvm: fix cr0 initialization on SIPI reset Avi Kivity
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