Re: kern/57199: Pure PVH i386 guests hang on disk activity

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR kern/57199; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Brad Spencer <brad%anduin.eldar.org@localhost>
Cc: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
        netbsd-bugs%netbsd.org@localhost, gdt%lexort.com@localhost
Subject: Re: kern/57199: Pure PVH i386 guests hang on disk activity
Date: Mon, 15 Jul 2024 18:36:41 +0200

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 On Mon, Jul 15, 2024 at 01:25:31PM +0200, Manuel Bouyer wrote:
 > I can reproduce a hang of the network interface, which may have the same
 > cause. Looks like an event is missed by the backend.
 > 
 > What is your dom0 ?
 
 Can you try the attached patch on your guest  ?
 With this my network hang is gone, and I can run your tar test to
 completion
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --
 
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 Index: include/hypervisor.h
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/xen/include/hypervisor.h,v
 retrieving revision 1.55.4.3
 diff -u -p -u -r1.55.4.3 hypervisor.h
 --- include/hypervisor.h	18 Oct 2023 16:53:03 -0000	1.55.4.3
 +++ include/hypervisor.h	15 Jul 2024 16:08:09 -0000
 @@ -108,13 +108,15 @@ struct xen_npx_attach_args {
   * The proper fix is to get upstream to stop assuming that all OSs use
   * mb(), rmb(), wmb().
   */
 +
  #undef xen_mb
  #undef xen_rmb
  #undef xen_wmb
  
 -#define xen_mb()  membar_sync()
 -#define xen_rmb() membar_acquire()
 -#define xen_wmb() membar_release()
 +#define xen_mb()  membar_sync(); asm volatile("mfence":::"memory");
 +#define xen_rmb() membar_acquire(); asm volatile("lfence":::"memory");
 +#define xen_wmb() membar_release(); asm volatile("sfence" ::: "memory");
 +
  #endif /* __XEN_INTERFACE_VERSION */
  
  #include <machine/xen/hypercalls.h>
 Index: include/xenring.h
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/xen/include/xenring.h,v
 retrieving revision 1.6.20.1
 diff -u -p -u -r1.6.20.1 xenring.h
 --- include/xenring.h	31 Jul 2023 15:23:02 -0000	1.6.20.1
 +++ include/xenring.h	15 Jul 2024 16:08:09 -0000
 @@ -24,9 +24,9 @@
  #undef xen_rmb
  #undef xen_wmb
  
 -#define xen_mb()  membar_sync()
 -#define xen_rmb() membar_acquire()
 -#define xen_wmb() membar_release()
 +#define xen_mb()  membar_sync(); asm volatile("mfence":::"memory");
 +#define xen_rmb() membar_acquire(); asm volatile("lfence":::"memory");
 +#define xen_wmb() membar_release(); asm volatile("sfence" ::: "memory");
  
  /*
   * Define ring types. These were previously part of the public API.
 
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