Re: [win-pv-devel] [PATCH] Avoid making hypercalls in the SyncWorker DPC

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Fabio Fantoni [mailto:fabio.fantoni@xxxxxxx]
> Sent: 21 November 2014 10:30
> To: Paul Durrant; win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [win-pv-devel] [PATCH] Avoid making hypercalls in the
> SyncWorker DPC
> 
> Il 20/11/2014 17:25, Paul Durrant ha scritto:
> > The code has to run with interrupts disabled on all CPUs apart from 0 to
> > corale them across a suspend/resume. Making hypercalls from within that
> > code is thus incompatible with re-populating the hypercall table on resume
> > since it transpites then Xen writes each byte in the page to 0xcc (int 3)
> > before actually setting up the hypercall thunks. The only hypercall that the
> > code was actually making was a SCHEDOP_yield and this is trivially replaced
> > by an _mm_pause intrinsic which calls through to SCHEDOP_yield in the
> > VMEXIT handler.
> Thanks for the patch, I tested it, 3 save/restore without crash for now
> and I not saw any regression, I'll report you if I'll see other crash.
> 
> There is another problem with the save/restore on windows that is
> driving me crazy for months:
> with qxl vga all works good except after save/restore that make domU
> "freeze" for 2-3 minutes on spice connect (always first time and
> occasional the others), on windows shutdown/reboot and probably other
> operations.
> I'm unable to found the exactly cause of that, is there a way to know if
> is caused by something unexpected in windows pv drivers or other xen
> particular things in xen save/restore? (for example "interrupts disabled
> on all CPUs apart from 0 to corale them across a suspend/resume" if I
> understand good).
> 

Is it a network issue? The PV drivers should re-generate gratuitous ARPs and 
IPv6 neighbour solicitations on resume so things should be ok but it would be 
worth un-firewalling ICMP so you can check whether the VM is actually pingable.
If the VM is really wedged though you can always use xen-hvmcrash from dom0 to 
try to forcibly crash the domain such that Windows will create a MEMORY.DMP 
that you can have a look at after reboot.

  Paul

> Thanks for any reply and sorry for my bad english.
> 
> >
> > Signed-off-by: Paul Durrant<paul.durrant@xxxxxxxxxx>
> > ---
> >   src/xenbus/sync.c | 14 +++++++-------
> >   1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/src/xenbus/sync.c b/src/xenbus/sync.c
> > index 41ecbf9..78b5bef 100644
> > --- a/src/xenbus/sync.c
> > +++ b/src/xenbus/sync.c
> > @@ -151,7 +151,7 @@ SyncWorker(
> >               break;
> >
> >           if (SyncContext.DisableInterrupts[Cpu] == InterruptsDisabled) {
> > -            SchedYield();
> > +            _mm_pause();
> >               KeMemoryBarrier();
> >
> >               continue;
> > @@ -171,7 +171,7 @@ SyncWorker(
> >               Attempts = 0;
> >               while (SyncContext.Sequence == Sequence &&
> >                      SyncContext.CompletionCount < CpuCount) {
> > -                SchedYield();
> > +                _mm_pause();
> >                   KeMemoryBarrier();
> >
> >                   if (++Attempts > 1000) {
> > @@ -213,7 +213,7 @@ SyncWorker(
> >
> >               while (SyncContext.Sequence == Sequence &&
> >                      SyncContext.CompletionCount < CpuCount) {
> > -                SchedYield();
> > +                _mm_pause();
> >                   KeMemoryBarrier();
> >               }
> >
> > @@ -268,7 +268,7 @@ SyncCapture(
> >       InterlockedIncrement(&SyncContext.CompletionCount);
> >
> >       while (SyncContext.CompletionCount < CpuCount) {
> > -        SchedYield();
> > +        _mm_pause();
> >           KeMemoryBarrier();
> >       }
> >
> > @@ -305,7 +305,7 @@ again:
> >
> >       Attempts = 0;
> >       while (SyncContext.CompletionCount < CpuCount) {
> > -        SchedYield();
> > +        _mm_pause();
> >           KeMemoryBarrier();
> >
> >           if (++Attempts > 1000) {
> > @@ -366,7 +366,7 @@ SyncEnableInterrupts(
> >       InterlockedIncrement(&SyncContext.CompletionCount);
> >
> >       while (SyncContext.CompletionCount < CpuCount) {
> > -        SchedYield();
> > +        _mm_pause();
> >           KeMemoryBarrier();
> >       }
> >
> > @@ -400,7 +400,7 @@ SyncRelease(
> >       InterlockedIncrement(&SyncContext.CompletionCount);
> >
> >       while (SyncContext.CompletionCount < CpuCount) {
> > -        SchedYield();
> > +        _mm_pause();
> >           KeMemoryBarrier();
> >       }
> >
> > -- 2.1.1


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