Re: [Xen-devel] [PATCH] x86/XPTI: fix S3 resume (and CPU offlining in general)

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/05/18 15:35, Simon Gaiser wrote:
> Andrew Cooper:
>> On 24/05/18 15:14, Simon Gaiser wrote:
>>> Jan Beulich:
>>>>>>> On 24.05.18 at 16:00, <simon@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>>> Jan Beulich:
>>>>>> In commit d1d6fc97d6 ("x86/xpti: really hide almost all of Xen image")
>>>>>> I've failed to remember the fact that multiple CPUs share a stub
>>>>>> mapping page. Therefore it is wrong to unconditionally zap the mapping
>>>>>> when bringing down a CPU; it may only be unmapped when no other online
>>>>>> CPU uses that same page.
>>>>>>
>>>>>> Reported-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
>>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>>>
>>>>>> --- a/xen/arch/x86/smpboot.c
>>>>>> +++ b/xen/arch/x86/smpboot.c
>>>>>> @@ -876,7 +876,21 @@ static void cleanup_cpu_root_pgt(unsigne
>>>>>>  
>>>>>>      free_xen_pagetable(rpt);
>>>>>>  
>>>>>> -    /* Also zap the stub mapping for this CPU. */
>>>>>> +    /*
>>>>>> +     * Also zap the stub mapping for this CPU, if no other online one 
>>>>>> uses
>>>>>> +     * the same page.
>>>>>> +     */
>>>>>> +    if ( stub_linear )
>>>>>> +    {
>>>>>> +        unsigned int other;
>>>>>> +
>>>>>> +        for_each_online_cpu(other)
>>>>>> +            if ( !((per_cpu(stubs.addr, other) ^ stub_linear) >> 
>>>>>> PAGE_SHIFT) )
>>>>>> +            {
>>>>>> +                stub_linear = 0;
>>>>>> +                break;
>>>>>> +            }
>>>>>> +    }
>>>>>>      if ( stub_linear )
>>>>>>      {
>>>>>>          l3_pgentry_t *l3t = l4e_to_l3e(common_pgt);
>>>>> Tried this on-top of staging (fc5805daef) and I still get the same
>>>>> double fault.
>>>> Hmm, it worked for me offlining (and later re-onlining) several pCPU-s. 
>>>> What
>>>> size a system are you testing on? Mine has got only 12 CPUs, i.e. all stubs
>>>> are in the same page (and I'd never unmap anything here at all).
>>> 4 cores + HT, so 8 CPUs from Xen's PoV.
>> Can you try with the "x86/traps: Dump the instruction stream even for
>> double faults" patch I've just posted, and show the full #DF panic log
>> please?  (Its conceivable that there are multiple different issues here.)
> With Jan's and your patch:
>
> (XEN) mce_intel.c:782: MCA Capability: firstbank 0, extended MCE MSR 0, 
> BCAST, CMCI
> (XEN) CPU0 CMCI LVT vector (0xf2) already installed
> (XEN) Finishing wakeup from ACPI S3 state.
> (XEN) Enabling non-boot CPUs  ...
> (XEN) emul-priv-op.c:1166:d0v1 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00000
> (XEN) emul-priv-op.c:1166:d0v1 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00800
> (XEN) emul-priv-op.c:1166:d0v2 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00000
> (XEN) emul-priv-op.c:1166:d0v2 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00800
> (XEN) emul-priv-op.c:1166:d0v3 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00000
> (XEN) emul-priv-op.c:1166:d0v3 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00800
> (XEN) emul-priv-op.c:1166:d0v4 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00000
> (XEN) emul-priv-op.c:1166:d0v4 Domain attempted WRMSR 0000001b from 
> 0x00000000fee00c00 to 0x00000000fee00800

/sigh - Naughty Linux.  The PVOps really ought to know that they don't
have an APIC to play with, not that this related to the crash.

> (XEN) *** DOUBLE FAULT ***
> (XEN) ----[ Xen-4.11-rc  x86_64  debug=y   Not tainted ]----
> (XEN) CPU:    0
> (XEN) RIP:    e008:[<ffff82d08037b964>] handle_exception+0x9c/0xff
> (XEN) RFLAGS: 0000000000010006   CONTEXT: hypervisor
> (XEN) rax: ffffc90040ce40d8   rbx: 0000000000000000   rcx: 0000000000000003
> (XEN) rdx: 0000000000000000   rsi: 0000000000000000   rdi: 0000000000000000
> (XEN) rbp: 000036ffbf31bf07   rsp: ffffc90040ce4000   r8:  0000000000000000
> (XEN) r9:  0000000000000000   r10: 0000000000000000   r11: 0000000000000000
> (XEN) r12: 0000000000000000   r13: 0000000000000000   r14: ffffc90040ce7fff
> (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4: 0000000000042660
> (XEN) cr3: 000000022200a000   cr2: ffffc90040ce3ff8
> (XEN) fsb: 00007fa9e7909740   gsb: ffff88021e740000   gss: 0000000000000000
> (XEN) ds: 002b   es: 002b   fs: 0000   gs: 0000   ss: e010   cs: e008
> (XEN) Xen code around <ffff82d08037b964> (handle_exception+0x9c/0xff):
> (XEN)  00 f3 90 0f ae e8 eb f9 <e8> 07 00 00 00 f3 90 0f ae e8 eb f9 83 e9 01 
> 75
> (XEN) Current stack base ffffc90040ce0000 differs from expected 
> ffff8300cec88000
> (XEN) Valid stack range: ffffc90040ce6000-ffffc90040ce8000, 
> sp=ffffc90040ce4000, tss.rsp0=ffff8300cec8ffa0
> (XEN) No stack overflow detected. Skipping stack trace.

Ok - this is the same as George's crash, and yes - I did misdiagnose the
stack we were on.  I presume this hardware doesn't have SMAP? (or we've
expected to take a #DF immediately at the head of the syscall hander.)

~Andrew

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