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

Avi Kivity
2010-04-27T13:37:45Z

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