Message-ID: <51E784CB.1040402@linux.vnet.ibm.com>
Date: Thu, 18 Jul 2013 14:01:47 +0800
From: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
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To: Gleb Natapov <gleb@redhat.com>
CC: markus@trippelsdorf.de, mtosatti@redhat.com, pbonzini@redhat.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: MMU: avoid fast page fault fixing mmio page fault
References: <1374123157-11142-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <20130718053154.GY11772@redhat.com>
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On 07/18/2013 01:31 PM, Gleb Natapov wrote:
> On Thu, Jul 18, 2013 at 12:52:37PM +0800, Xiao Guangrong wrote:
>> Currently, fast page fault tries to fix mmio page fault when the
>> generation number is invalid (spte.gen != kvm.gen) and returns to
>> guest to retry the fault since it sees the last spte is nonpresent
>> which causes infinity loop
>>
>> It can be triggered only on AMD host since the mmio page fault is
>> recognized as ept-misconfig
>>
> We still call into regular page fault handler from ept-misconfig
> handler, but fake zero error_code we provide makes page_fault_can_be_fast()
> return false.

Yes.

> 
> Shouldn't shadow paging trigger this too? I haven't encountered this on
> Intel without ept.

Since currently fast page fault only works for direct mmu. :)

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