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

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Date:   Mon, 26 Aug 2019 19:39:06 +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 06:47:57PM +0800, Peter Xu wrote:
> 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?

Sorry, it should be s/shadow paging/NPT/...

[root@...dl385g10-10 peter]# ./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:138: false
  pid=5433 tid=5436 - Success
     1  0x0000000000401cc1: vcpu_worker at dirty_log_test.c:138
     2  0x00007f18977992dd: ?? ??:0
     3  0x00007f18974ca132: ?? ??:0
  Invalid guest sync status: exit_reason=SHUTDOWN

[root@...dl385g10-10 peter]# modprobe -r kvm_amd
[root@...dl385g10-10 peter]# modprobe kvm_amd npt=0
[root@...dl385g10-10 peter]# ./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
Dirtied 102400 pages
Total bits checked: dirty (99021), clear (8027939), track_next (23425)

> 
> 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