Re: [Xen-devel] Weird altp2m behaviour when switching early to a new view

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 04/16/2018 08:47 PM, George Dunlap wrote:
> On 04/13/2018 03:44 PM, Razvan Cojocaru wrote:
>> On 04/11/2018 11:04 AM, Razvan Cojocaru wrote:
>>> Debugging continues.
>>
>> Finally, the attached patch seems to get the display unstuck in my
>> scenario, although for one guest I get:
>>
>> (XEN) d2v0 Unexpected vmexit: reason 49
>> (XEN) domain_crash called from vmx.c:4120
>> (XEN) Domain 2 (vcpu#0) crashed on cpu#1:
>> (XEN) ----[ Xen-4.11-unstable  x86_64  debug=y   Not tainted ]----
>> (XEN) CPU:    1
>> (XEN) RIP:    0010:[<fffff96000842354>]
>> (XEN) RFLAGS: 0000000000010246   CONTEXT: hvm guest (d2v0)
>> (XEN) rax: fffff88003000000   rbx: fffff900c0083db0   rcx: 00000000aa55aa55
>> (XEN) rdx: fffffa80041bdc41   rsi: fffff900c00c69a0   rdi: 0000000000000001
>> (XEN) rbp: 0000000000000000   rsp: fffff88002ee9ef0   r8:  fffffa80041bdc40
>> (XEN) r9:  fffff80001810e80   r10: fffffa800342aa70   r11: fffff88002ee9e80
>> (XEN) r12: 0000000000000005   r13: 0000000000000001   r14: fffff900c00c08b0
>> (XEN) r15: 0000000000000001   cr0: 0000000080050031   cr4: 00000000000406f8
>> (XEN) cr3: 00000000ef771000   cr2: fffff900c00c8000
>> (XEN) fsb: 00000000fffde000   gsb: fffff80001810d00   gss: 000007fffffdc000
>> (XEN) ds: 002b   es: 002b   fs: 0053   gs: 002b   ss: 0018   cs: 0010
>>
>> i.e. EXIT_REASON_EPT_MISCONFIG - so not of the woods yet. I am hoping
>> somebody more familiar with the code can point to a more elegant
>> solution if one exists.
> 
> I think I have an idea what's going on, but it's complicated. :-)
> 
> Basically, the logdirty functionality isn't simple, and needs careful
> thought on how to integrate it.  I'll write some more tomorrow, and see
> if I can come up with a solution.

I think I know why this happens for the one guest - the other guests
start at a certain resolution display-wise and stay that way until shutdown.

This particular guest starts with a larger screen, then goes to roughly
2/3rds of it, then tries to go back to the initial larger one - at which
point the above happens. I assume this corresponds to some pages being
removed and/or added. I'll test this theory more tomorrow - if it's
correct I should be able to reproduce the crash (with the patch) by
simply resetting the screen resolution (increasing it).


Thanks,
Razvan

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