Re: [Xen-devel] SOLVED - Infinte loop in RtlPrefetchMemoryNonTemporal underWindows

["Jean Guyader" <jean.guyader@xxxxxxxxx>]

James,

That should be fixed be the changeset 18512.
Does your libxc is up to date ?

2008/11/22 James Harper <james.harper@xxxxxxxxxxxxxxxx>:
> I fixed this with the following entry in my config:
>
> cpuid =
> ['0x80000005:ecx=xxxxxxxxxxxxxxxxxxxxxxxxkkkkkkkk,edx=xxxxxxxxxxxxxxxxxx
> xxxxxxkkkkkkkk']
>
> This passes through the physical host value of the relevant cache
> information cpuid function to the DomU.
>
> Is there any reason why we wouldn't want to do this? I think I'm working
> around what is actually a bug. Intel CPU's seem to keep cache
> information in another cpuid function so maybe it is only (some?) AMD
> cpu's affected?
>
> As per the email below, under some circumstances (eg when I give Windows
> a pre-checksum-verified packet) it makes a call to a function called
> RtlPrefetchMemoryNonTemporal which uses the cache line size as a
> decrement in a loop. Xen is setting the cache line size to zero (at
> least for AMD processors) causing that loop to never terminate.
>
> James
>
>> -----Original Message-----
>> From: James Harper
>> Sent: Saturday, 22 November 2008 23:00
>> To: James Harper; xen-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: RE: [Xen-devel] Infinte loop in RtlPrefetchMemoryNonTemporal
>> underWindows
>>
>> > I have been trying to track down a problem that occurs when my GPLPV
>> > drivers give Windows a packet with the
> NdisPacketTcpChecksumSucceeded
>> > flag set. The problem is that the machine locks hard.
>> >
>> > After some tedious work with the debugger, I have found that Windows
>> > makes a call to a routine called RtlPrefetchMemoryNonTemporal, which
>> > looks like this:
>> >
>> > 8088e579 mov     eax,dword ptr [nt!KePrefetchNTAGranularity 8088e57e
>> > 0f184100 prefetchnta [ecx]
>> > 8088e582 add     ecx,eax
>> > 8088e584 sub     edx,eax
>> > 8088e586 ja      nt!RtlPrefetchMemoryNonTemporal+0x6 (8088e57e)
>> > 8088e588 ret
>> >
>> > Unfortunately it appears that the value at
> nt!KePrefetchNTAGranularity
>> > is 0, hence the infinite loop.
>> >
>>
>> A bit more debugging shows that RtlPrefectMemoryNonTemporal starts out
>> life like this:
>>
>> nt!RtlPrefetchMemoryNonTemporal:
>> 8088e578 ret
>> 8088e579 mov     eax,dword ptr [nt!KePrefetchNTAGranularity 8088e57e
>> 0f184100 prefetchnta [ecx]
>> 8088e582 add     ecx,eax
>> 8088e584 sub     edx,eax
>> 8088e586 ja      nt!RtlPrefetchMemoryNonTemporal+0x6 (8088e57e)
>> 8088e588 ret
>>
>> But then for some reason becomes:
>>
>> nt!RtlPrefetchMemoryNonTemporal:
>> 8088e578 nop
>> 8088e579 mov     eax,dword ptr [nt!KePrefetchNTAGranularity 8088e57e
>> 0f184100 prefetchnta [ecx]
>> 8088e582 add     ecx,eax
>> 8088e584 sub     edx,eax
>> 8088e586 ja      nt!RtlPrefetchMemoryNonTemporal+0x6 (8088e57e)
>> 8088e588 ret
>>
>> The difference being that the initial ret becomes a nop...
>>
>> This is getting stranger and stranger.
>>
>> James
>
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>



-- 
Jean Guyader

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