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

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Date:   Mon, 26 Aug 2019 18:47:57 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Huth <thuth@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: selftests: Detect max PA width from cpuid

On Mon, Aug 26, 2019 at 10:25:55AM +0200, Vitaly Kuznetsov wrote:
> Peter Xu <peterx@...hat.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