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| author | Rusty Russell <rusty@rustcorp.com.au> | 2013-07-02 15:35:13 +0930 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2013-07-02 15:42:04 +0930 |
| commit | 8fd9a6365eb8a79a2d8f0e0baa01f4db6345e8dd (patch) | |
| tree | 35b566aed74e6b4c46cdbff23b2ceda5f4fe5a9b | |
| parent | 8c6bab4f3874d31804a00782c48a8f244a0d3cc0 (diff) | |
tools/lguest: fix missing rmb().
The virtio spec was missing a barrier in example code, so I went back
to look at the lguest code. Indeed, we need one.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
| -rw-r--r-- | tools/lguest/lguest.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/tools/lguest/lguest.c b/tools/lguest/lguest.c index 07a03452c227..49ed25b5bbb9 100644 --- a/tools/lguest/lguest.c +++ b/tools/lguest/lguest.c @@ -177,6 +177,7 @@ static struct termios orig_term; * in precise order. */ #define wmb() __asm__ __volatile__("" : : : "memory") +#define rmb() __asm__ __volatile__("" : : : "memory") #define mb() __asm__ __volatile__("" : : : "memory") /* Wrapper for the last available index. Makes it easier to change. */ @@ -676,6 +677,12 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq, errx(1, "Guest moved used index from %u to %u", last_avail, vq->vring.avail->idx); + /* + * Make sure we read the descriptor number *after* we read the ring + * update; don't let the cpu or compiler change the order. + */ + rmb(); + /* * Grab the next descriptor number they're advertising, and increment * the index we've seen. @@ -695,6 +702,12 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq, i = head; /* + * We have to read the descriptor after we read the descriptor number, + * but there's a data dependency there so the CPU shouldn't reorder + * that: no rmb() required. + */ + + /* * If this is an indirect entry, then this buffer contains a descriptor * table which we handle as if it's any normal descriptor chain. */ |