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

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Date:   Mon, 26 Aug 2019 13:34:44 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Peter Xu <peterx@...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

Peter Xu <peterx@...hat.com> writes:

> 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?
>

Yep,

test passes with shadow paging, fails when NPT is enabled.


> 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.

Sounds like a bug indeed.

-- 
Vitaly