diff options
| author |   mikeb <mikeb@openbsd.org> | 2016-08-03 14:55:57 +0000 |
|---|---|---|
| committer | mikeb <mikeb@openbsd.org> | 2016-08-03 14:55:57 +0000 |
| commit | 4ef38d8395a08772f177cd28a89917eb0fc1960d (patch) | |
| tree | caa6aa1f3fd6018dd25bc382506e06e56f63df2b | |
| parent | Fold umass_atapi_attach() and umass_scsi_setup() into umass_scsi_attach() to (diff) | |
| download | wireguard-openbsd-4ef38d8395a08772f177cd28a89917eb0fc1960d.tar.xz wireguard-openbsd-4ef38d8395a08772f177cd28a89917eb0fc1960d.zip | |
Use an atomic operation to clear pending event bits
Pending event bits are located in a shared memory and are potentially
accessed by multiple CPUs running dom0 and the guest VM. It appears
that a failure to synchronize changes to this shared memory leads to
race conditions resulting in the guest missing out on notifications.
| -rw-r--r-- | sys/dev/pv/xen.c | 6 | ||||
| -rw-r--r-- | sys/dev/pv/xenreg.h | 6 | ||||
| -rw-r--r-- | sys/dev/pv/xenvar.h | 14 |
3 files changed, 19 insertions, 7 deletions
diff --git a/sys/dev/pv/xen.c b/sys/dev/pv/xen.c index c12328cd0d1..8f4be60e649 100644 --- a/sys/dev/pv/xen.c +++ b/sys/dev/pv/xen.c @@ -1,4 +1,4 @@ -/* $OpenBSD: xen.c,v 1.58 2016/08/01 14:37:39 mikeb Exp $ */ +/* $OpenBSD: xen.c,v 1.59 2016/08/03 14:55:57 mikeb Exp $ */ /* * Copyright (c) 2015 Mike Belopuhov @@ -633,8 +633,8 @@ xen_intr(void) for (bit = 0; pending > 0; pending >>= 1, bit++) { if ((pending & 1) == 0) continue; - sc->sc_ipg->evtchn_pending[row] &= ~(1 << bit); - virtio_membar_producer(); + atomic_clearbit_ptr(&sc->sc_ipg->evtchn_pending[row], + bit); port = (row * LONG_BIT) + bit; if ((xi = xen_lookup_intsrc(sc, port)) == NULL) { printf("%s: unhandled interrupt on port %u\n", diff --git a/sys/dev/pv/xenreg.h b/sys/dev/pv/xenreg.h index e6cc81891ab..b68ed762800 100644 --- a/sys/dev/pv/xenreg.h +++ b/sys/dev/pv/xenreg.h @@ -1,4 +1,4 @@ -/* $OpenBSD: xenreg.h,v 1.8 2016/01/18 19:06:48 mikeb Exp $ */ +/* $OpenBSD: xenreg.h,v 1.9 2016/08/03 14:55:57 mikeb Exp $ */ /* * Permission is hereby granted, free of charge, to any person obtaining a copy @@ -237,8 +237,8 @@ struct shared_info { * per-vcpu selector word to be set. Each bit in the selector covers a * 'C long' in the PENDING bitfield array. */ - unsigned long evtchn_pending[sizeof(unsigned long) * 8]; - unsigned long evtchn_mask[sizeof(unsigned long) * 8]; + volatile unsigned long evtchn_pending[sizeof(unsigned long) * 8]; + volatile unsigned long evtchn_mask[sizeof(unsigned long) * 8]; /* * Wallclock time: updated only by control software. Guests should diff --git a/sys/dev/pv/xenvar.h b/sys/dev/pv/xenvar.h index d4e3fc5fc9d..a3cb403499a 100644 --- a/sys/dev/pv/xenvar.h +++ b/sys/dev/pv/xenvar.h @@ -1,4 +1,4 @@ -/* $OpenBSD: xenvar.h,v 1.33 2016/07/29 21:27:43 mikeb Exp $ */ +/* $OpenBSD: xenvar.h,v 1.34 2016/08/03 14:55:58 mikeb Exp $ */ /* * Copyright (c) 2015 Mike Belopuhov @@ -143,6 +143,18 @@ struct xs_transaction { struct xs_softc *xst_sc; }; +static inline int +atomic_clearbit_ptr(volatile void *ptr, int bit) +{ + int obit; + + __asm__ __volatile__ ("lock btrl %2,%1; sbbl %0,%0" : + "=r" (obit), "=m" (*(volatile long *)ptr) : "Ir" (bit) : + "memory"); + + return (obit); +} + int xs_cmd(struct xs_transaction *, int, const char *, struct iovec **, int *); void xs_resfree(struct xs_transaction *, struct iovec *, int); |