Re: [PATCH] KVM: selftests: Detect max PA width from cpuid

Peter Xu
2019-08-26T10:48:12Z

On Mon, Aug 26, 2019 at 10:25:55AM +0200, Vitaly Kuznetsov wrote:
> Peter Xu <peterx@redhat.com> writes:
>
> > The dirty_log_test is failing on some old machines like Xeon E3-1220
> > with tripple faults when writting to the tracked memory region:
>
> s,writting,writing,
>
> >
> > Test iterations: 32, interval: 10 (ms)
> > Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
> > guest physical test memory offset: 0x7fbffef000
> > ==== Test Assertion Failure ====
> > dirty_log_test.c:138: false
> > pid=6137 tid=6139 - Success
> > 1 0x0000000000401ca1: vcpu_worker at dirty_log_test.c:138
> > 2 0x00007f3dd9e392dd: ?? ??:0
> > 3 0x00007f3dd9b6a132: ?? ??:0
> > Invalid guest sync status: exit_reason=SHUTDOWN
> >
>
> This patch breaks on my AMD machine with
>
> # cpuid -1 -l 0x80000008
> CPU:
> Physical Address and Linear Address Size (0x80000008/eax):
> maximum physical address bits = 0x30 (48)
> maximum linear (virtual) address bits = 0x30 (48)
> maximum guest physical address bits = 0x0 (0)
>
>
> Pre-patch:
>
> # ./dirty_log_test
> Test iterations: 32, interval: 10 (ms)
> Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
> guest physical test memory offset: 0x7fbffef000
> Dirtied 139264 pages
> Total bits checked: dirty (135251), clear (7991709), track_next (29789)
>
> Post-patch:
>
> # ./dirty_log_test
> Test iterations: 32, interval: 10 (ms)
> Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
> Supported guest physical address width: 48
> guest physical test memory offset: 0xffffbffef000
> ==== Test Assertion Failure ====
> dirty_log_test.c:141: false
> pid=77983 tid=77985 - Success
> 1 0x0000000000401d12: vcpu_worker at dirty_log_test.c:138
> 2 0x00007f636374358d: ?? ??:0
> 3 0x00007f63636726a2: ?? ??:0
> Invalid guest sync status: exit_reason=SHUTDOWN

Vitaly,

Are you using shadow paging? If so, could you try NPT=off?

I finally found a AMD host and I also found that it's passing with
shadow MMU mode which is strange. If so I would suspect it's a real
bug in AMD NTP path but I'd like to see whether it's also happening on
your side.

Thanks,

--
Peter Xu