linux-kernel - Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

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Message-ID: <4BD6E8A6.5040008@redhat.com>
Date:	Tue, 27 Apr 2010 16:37:42 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

On 04/27/2010 04:28 PM, Joerg Roedel wrote:
>
>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>> index d9dfc8c..8426870 100644
>>> --- a/arch/x86/include/asm/kvm_host.h
>>> +++ b/arch/x86/include/asm/kvm_host.h
>>> @@ -298,6 +298,9 @@ struct kvm_vcpu_arch {
>>>   	/* Used for two dimensional paging emulation */
>>>   	struct kvm_mmu nested_mmu;
>>>
>>> +	unsigned long fault_address;
>>>        
>> Probably a problem on i386.  How does npt handle faults when the
>> guest is using pae paging and the host (in our case the guest...)
>> isn't?  I see it uses exit_info_2 for the address, which is a u64.
>>      
> This shouldn't be an issue. If we run on 32bit host with nested paging
> the guest can't have more than 4gb of addressable memory because of the
> page table limitations (nested page table is always in host format).
>    

But the nested guest can use pae paging and generate a #NPF with 
exit_info_2 > 4GB.  So we need to keep the full fault address; if we 
truncate, the guest might actually resolve the fault and let the nested 
guest continue.

-- 
error compiling committee.c: too many arguments to function

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