42 lines
1.5 KiB
Diff
42 lines
1.5 KiB
Diff
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From c1fce65e2b720684ea6ba76ae59921542bd154bb Mon Sep 17 00:00:00 2001
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From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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Date: Fri, 20 Nov 2015 12:22:14 -0500
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Subject: [PATCH 3/3] libvchan: Read prod/cons only once.
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We must ensure that the prod/cons are only read once and that
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the compiler won't try to optimize the reads. That is split
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the read of these in multiple instructions influencing later
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branch code. As such insert barriers when fetching the cons
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and prod index.
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This is part of XSA155.
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Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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---
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tools/libvchan/io.c | 2 ++
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1 file changed, 2 insertions(+)
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diff --git a/tools/libvchan/io.c b/tools/libvchan/io.c
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index 8a9629b..381cc05 100644
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--- a/tools/libvchan/io.c
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+++ b/tools/libvchan/io.c
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@@ -117,6 +117,7 @@ static inline int send_notify(struct libxenvchan *ctrl, uint8_t bit)
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static inline int raw_get_data_ready(struct libxenvchan *ctrl)
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{
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uint32_t ready = rd_prod(ctrl) - rd_cons(ctrl);
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+ xen_mb(); /* Ensure 'ready' is read only once. */
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if (ready > rd_ring_size(ctrl))
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/* We have no way to return errors. Locking up the ring is
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* better than the alternatives. */
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@@ -158,6 +159,7 @@ int libxenvchan_data_ready(struct libxenvchan *ctrl)
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static inline int raw_get_buffer_space(struct libxenvchan *ctrl)
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{
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uint32_t ready = wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
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+ xen_mb(); /* Ensure 'ready' is read only once. */
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if (ready > wr_ring_size(ctrl))
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/* We have no way to return errors. Locking up the ring is
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* better than the alternatives. */
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--
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2.1.0
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