Re: [Xen-devel] Deadlock in stdvga_mem_accept() with emulation

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Razvan Cojocaru [mailto:rcojocaru@xxxxxxxxxxxxxxx]
> Sent: 13 July 2015 10:42
> To: Paul Durrant; Andrew Cooper; xen-devel@xxxxxxxxxxxxx
> Cc: Keir (Xen.org); Jan Beulich
> Subject: Re: [Xen-devel] Deadlock in stdvga_mem_accept() with emulation
> 
> On 07/13/2015 12:05 PM, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Razvan Cojocaru [mailto:rcojocaru@xxxxxxxxxxxxxxx]
> >> Sent: 13 July 2015 10:03
> >> To: Paul Durrant; Andrew Cooper; xen-devel@xxxxxxxxxxxxx
> >> Cc: Keir (Xen.org); Jan Beulich
> >> Subject: Re: [Xen-devel] Deadlock in stdvga_mem_accept() with
> emulation
> >>
> >> On 07/13/2015 12:01 PM, Paul Durrant wrote:
> >>>> -----Original Message-----
> >>>> From: Razvan Cojocaru [mailto:rcojocaru@xxxxxxxxxxxxxxx]
> >>>> Sent: 13 July 2015 09:50
> >>>> To: Andrew Cooper; xen-devel@xxxxxxxxxxxxx
> >>>> Cc: Keir (Xen.org); Jan Beulich; Paul Durrant
> >>>> Subject: Re: Deadlock in stdvga_mem_accept() with emulation
> >>>>
> >>>> On 07/13/2015 11:10 AM, Andrew Cooper wrote:
> >>>>> On 13/07/2015 08:48, Razvan Cojocaru wrote:
> >>>>>> Hello,
> >>>>>>
> >>>>>> I'm battling the following hypervisor crash with current staging:
> >>>>>>
> >>>>>> (d2) Invoking ROMBIOS ...
> >>>>>> (XEN) stdvga.c:147:d2v0 entering stdvga and caching modes
> >>>>>> (d2) VGABios $Id: vgabios.c,v 1.67 2008/01/27 09:44:12 vruppert Exp
> $
> >>>>>> (XEN) Watchdog timer detects that CPU7 is stuck!
> >>>>>> (XEN) ----[ Xen-4.6-unstable  x86_64  debug=y  Not tainted ]----
> >>>>>> (XEN) CPU:    7
> >>>>>> (XEN) RIP:    e008:[<ffff82d08012c3f1>] _spin_lock+0x31/0x54
> >>>>>> (XEN) RFLAGS: 0000000000000202   CONTEXT: hypervisor (d2v0)
> >>>>>> (XEN) rax: 000000000000c11d   rbx: ffff83041e687970   rcx:
> >>>> 000000000000c11e
> >>>>>> (XEN) rdx: ffff83041e687970   rsi: 000000000000c11e   rdi:
> >> ffff83041e687978
> >>>>>> (XEN) rbp: ffff83040eb37208   rsp: ffff83040eb37200   r8:
> >>>> 0000000000000000
> >>>>>> (XEN) r9:  0000000000000000   r10: ffff82d08028c3c0   r11:
> >>>> 0000000000000000
> >>>>>> (XEN) r12: ffff83041e687000   r13: ffff83041e687970   r14:
> >> ffff83040eb37278
> >>>>>> (XEN) r15: 00000000000c253f   cr0: 000000008005003b   cr4:
> >>>> 00000000001526e0
> >>>>>> (XEN) cr3: 00000004054a0000   cr2: 0000000000000000
> >>>>>> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: 0000   cs: e008
> >>>>>> (XEN) Xen stack trace from rsp=ffff83040eb37200:
> >>>>>> (XEN)    ffff83040eb37278 ffff83040eb37238 ffff82d0801d09b6
> >>>> 0000000000000282
> >>>>>> (XEN)    0000000000000008 ffff830403791bf0 ffff83041e687000
> >>>> ffff83040eb37268
> >>>>>> (XEN)    ffff82d0801cb23a 00000000000c253f ffff8300d85fc000
> >>>> 0000000000000001
> >>>>>> (XEN)    00000000000000c2 ffff83040eb37298 ffff82d0801cb410
> >>>> 00000000000c253f
> >>>>>> (XEN)    0000000000000000 0000000100000001 0100000000000000
> >>>> ffff83040eb37328
> >>>>>> (XEN)    ffff82d0801c2403 ffff83040eb37394 ffff83040eb30000
> >>>> 0000000000000000
> >>>>>> (XEN)    ffff83040eb37360 00000000000000c2 ffff8304054cb000
> >>>> 000000000000053f
> >>>>>> (XEN)    0000000000000002 0000000000000000 ffff83040eb373f4
> >>>> 00000000000000c2
> >>>>>> (XEN)    ffff83040eb373d8 0000000000000000 0000000000000000
> >>>> ffff82d08028c620
> >>>>>> (XEN)    0000000000000000 ffff83040eb37338 ffff82d0801c3e5d
> >>>> ffff83040eb37398
> >>>>>> (XEN)    ffff82d0801cb107 000000010eb37394 ffff830403791bf0
> >>>> ffff830403791bf0
> >>>>>> (XEN)    ffff83041e687000 ffff83040eb37398 ffff830403791bf0
> >>>> 0000000000000001
> >>>>>> (XEN)    ffff83040eb373d8 0000000000000001 00000000000c253f
> >>>> ffff83040eb373c8
> >>>>>> (XEN)    ffff82d0801cb291 ffff83040eb37b30 ffff8300d85fc000
> >>>> 0000000000000001
> >>>>>> (XEN)    0000000000000000 ffff83040eb37428 ffff82d0801bb440
> >>>> 00000000000a0001
> >>>>>> (XEN)    00000000000c253f 0000000100000001 0111000000000000
> >>>> ffff83040eb37478
> >>>>>> (XEN)    0000000000000001 0000000000000000 0000000000000000
> >>>> 0000000000000001
> >>>>>> (XEN)    0000000000000001 ffff83040eb374a8 ffff82d0801bc0b9
> >>>> 0000000000000001
> >>>>>> (XEN)    00000000000c253f ffff8300d85fc000 00000000000a0001
> >>>> 0100000000000000
> >>>>>> (XEN)    ffff83040eb37728 ffff82e00819dc60 0000000000000000
> >>>> ffff83040eb374c8
> >>>>>> (XEN) Xen call trace:
> >>>>>> (XEN)    [<ffff82d08012c3f1>] _spin_lock+0x31/0x54
> >>>>>> (XEN)    [<ffff82d0801d09b6>] stdvga_mem_accept+0x3b/0x125
> >>>>>> (XEN)    [<ffff82d0801cb23a>] hvm_find_io_handler+0x68/0x8a
> >>>>>> (XEN)    [<ffff82d0801cb410>] hvm_mmio_internal+0x37/0x67
> >>>>>> (XEN)    [<ffff82d0801c2403>] __hvm_copy+0xe9/0x37d
> >>>>>> (XEN)    [<ffff82d0801c3e5d>]
> hvm_copy_from_guest_phys+0x14/0x16
> >>>>>> (XEN)    [<ffff82d0801cb107>]
> hvm_process_io_intercept+0x10b/0x1d6
> >>>>>> (XEN)    [<ffff82d0801cb291>] hvm_io_intercept+0x35/0x5b
> >>>>>> (XEN)    [<ffff82d0801bb440>] hvmemul_do_io+0x1ff/0x2c1
> >>>>>> (XEN)    [<ffff82d0801bc0b9>] hvmemul_do_io_addr+0x117/0x163
> >>>>>> (XEN)    [<ffff82d0801bc129>] hvmemul_do_mmio_addr+0x24/0x26
> >>>>>> (XEN)    [<ffff82d0801bcbb5>] hvmemul_rep_movs+0x1ef/0x335
> >>>>>> (XEN)    [<ffff82d080198b49>] x86_emulate+0x56c9/0x13088
> >>>>>> (XEN)    [<ffff82d0801bbd26>] _hvm_emulate_one+0x186/0x281
> >>>>>> (XEN)    [<ffff82d0801bc1e8>] hvm_emulate_one+0x10/0x12
> >>>>>> (XEN)    [<ffff82d0801cb63e>] handle_mmio+0x54/0xd2
> >>>>>> (XEN)    [<ffff82d0801cb700>]
> >> handle_mmio_with_translation+0x44/0x46
> >>>>>> (XEN)    [<ffff82d0801c27f6>]
> >> hvm_hap_nested_page_fault+0x15f/0x589
> >>>>>> (XEN)    [<ffff82d0801e9741>] vmx_vmexit_handler+0x150e/0x188d
> >>>>>> (XEN)    [<ffff82d0801ee7d1>] vmx_asm_vmexit_handler+0x41/0xc0
> >>>>>> (XEN)
> >>>>>> (XEN)
> >>>>>> (XEN) ****************************************
> >>>>>> (XEN) Panic on CPU 7:
> >>>>>> (XEN) FATAL TRAP: vector = 2 (nmi)
> >>>>>> (XEN) [error_code=0000]
> >>>>>> (XEN) ****************************************
> >>>>>>
> >>>>>> At first I thought it was caused by V5 of the vm_event-based
> >>>>>> introspection series, but I've rolled it back enough to apply V4 on top
> >>>>>> of it (which has been thoroughly tested on Thursday), and it still
> >>>>>> happens, so this would at least appear to be unrelated at this point
> >>>>>> (other than the fact that our use case is maybe somewhat unusual
> with
> >>>>>> heavy emulation).
> >>>>>>
> >>>>>> I'll keep digging, but since this is a busy time for Xen I thought I'd
> >>>>>> issue a heads-up here as soon as possible, in case the problem is
> >>>>>> obvious for somebody and it helps getting it fixed sooner.
> >>>>>
> >>>>> In c/s 3bbaaec09b1b942f5624dee176da6e416d31f982 there is now a
> >>>>> deliberate split between stdvga_mem_accept() and
> >>>> stdvga_mem_complete()
> >>>>> about locking and unlocking the stdvga lock.
> >>>>>
> >>>>> At a guess, the previous chain of execution accidentally omitted the
> >>>>> stdvga_mem_complete() call.
> >>>>
> >>>> Thanks, I've reverted that patch and the crash is gone. I'll be happy to
> >>>> test a fix if one is provided, but I don't know enough about that code
> >>>> to go mess with it...
> >>>>
> >>>
> >>> The problem appears to be that __hvm_copy() is calling this code before
> >> establishing the type of the page:
> >>>
> >>>         /*
> >>>          * No need to do the P2M lookup for internally handled MMIO,
> >> benefiting
> >>>          * - 32-bit WinXP (& older Windows) on AMD CPUs for LAPIC
> accesses,
> >>>          * - newer Windows (like Server 2012) for HPET accesses.
> >>>          */
> >>>         if ( !nestedhvm_vcpu_in_guestmode(curr)
> >>>              && is_hvm_vcpu(curr)
> >>>              && hvm_mmio_internal(gpa) )
> >>>             return HVMCOPY_bad_gfn_to_mfn;
> >>>
> >>> ...and that call to hvm_mmio_internal is trying to re-acquire the lock. 
> >>> The
> >> big question is why on earth was I not hitting this every time in testing
> too...
> >> This patch series has gone through some pretty rigorous tests. Anyway, I
> will
> >> post a fix very shortly (since I know what needs to be done).
> >>>
> >>>   Paul
> >>
> >> Thanks Paul! I appreciate the quick response.
> >>
> >
> > While I'm prepping, try this:
> >
> > diff --git a/xen/arch/x86/hvm/stdvga.c b/xen/arch/x86/hvm/stdvga.c
> > index ebb3b42..08c797c 100644
> > --- a/xen/arch/x86/hvm/stdvga.c
> > +++ b/xen/arch/x86/hvm/stdvga.c
> > @@ -490,11 +490,18 @@ static bool_t stdvga_mem_accept(const struct
> hvm_io_handle
> >  {
> >      struct hvm_hw_stdvga *s = &current->domain-
> >arch.hvm_domain.stdvga;
> >
> > +    /*
> > +     * The range check must be done without taking any locks, to avoid
> > +     * deadlock when hvm_mmio_internal() is called from
> > +     * hvm_copy_to/from_guest_phys() in hvm_process_io_intercept().
> > +     */
> > +    if ( (hvm_mmio_first_byte(p) < VGA_MEM_BASE) ||
> > +         (hvm_mmio_last_byte(p) >= (VGA_MEM_BASE + VGA_MEM_SIZE))
> )
> > +        return 0;
> > +
> >      spin_lock(&s->lock);
> >
> > -    if ( !s->stdvga ||
> > -         (hvm_mmio_first_byte(p) < VGA_MEM_BASE) ||
> > -         (hvm_mmio_last_byte(p) >= (VGA_MEM_BASE + VGA_MEM_SIZE)) )
> > +    if ( !s->stdvga )
> >          goto reject;
> >
> >      if ( p->dir == IOREQ_WRITE && p->count > 1 )
> 
> The crash is gone, so in that respect:
> 
> Tested-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> 
> But my guest seems stuck at boot for some reason, the last line of xl
> dmesg is:
> 
> (XEN) stdvga.c:151:d3v0 leaving stdvga mode
> 
> and this is the guest state:
> 
> # ./xenctx -a 3
> rip: fffff80001497de0
> flags: 00000002 nz
> rsp: fffff80001479538
> rax: 0000000000000000   rcx: 00000000000003fe   rdx: 00000000000003fe
> rbx: fffff8000149a110   rsi: fffff80001479601   rdi: 0000000000009860
> rbp: 0000000000000000    r8: fffff8000149a174    r9: 0000000000000000
> r10: 00000000000027d7   r11: fffff800014795a0   r12: 0000000000000000
> r13: 0000000000000004   r14: 0000000000000002   r15: 0000000000000000
>  cs: 0010        ss: 0018        ds: 002b        es: 002b
>  fs: 0053 @ 0000000000000000
>  gs: 002b @ fffff80001805d00/fffff80001805d00
> 
> cr0: 0000000080050031
> cr2: 0000000000000030
> cr3: 0000000000187000
> cr4: 00000000000006b8
> 
> dr0: 0000000000000000
> dr1: 0000000000000000
> dr2: 0000000000000000
> dr3: 0000000000000000
> dr6: 00000000fffe0ff0
> dr7: 0000000000000400
> Code (instr addr fffff80001497de0)
> 90 8a c2 0f b7 d1 ee c3 90 90 90 90 90 90 90 90 90 0f b7 d1 ec <c3> 90
> 90 90 90 90 90 90 88 11 f0
> 
> But it's too early to tell that this isn't something my V5 code is now
> doing, so I'll come back if it turns out to be unrelated.
> 

I'm setting up my test rig again now.

  Paul

> 
> Thanks,
> Razvan

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