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Re: [Xen-devel] [PATCH v2 32/32] virtio_ring: use virt_store_mb
- To: "Michael S. Tsirkin" <mst@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx
- From: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
- Date: Fri, 1 Jan 2016 20:23:46 +0300
- Cc: linux-mips@xxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, sparclinux@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, Arnd Bergmann <arnd@xxxxxxxx>, x86@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxx>, linux-xtensa@xxxxxxxxxxxxxxxx, user-mode-linux-devel@xxxxxxxxxxxxxxxxxxxxx, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, adi-buildroot-devel@xxxxxxxxxxxxxxxxxxxxx, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-metag@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, linuxppc-dev@xxxxxxxxxxxxxxxx, David Miller <davem@xxxxxxxxxxxxx>
- Delivery-date: Fri, 01 Jan 2016 17:24:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
Hello.
On 12/31/2015 10:09 PM, Michael S. Tsirkin wrote:
We need a full barrier after writing out event index, using
virt_store_mb there seems better than open-coding. As usual, we need a
wrapper to account for strong barriers.
It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
include/linux/virtio_ring.h | 12 ++++++++++++
drivers/virtio/virtio_ring.c | 15 +++++++++------
2 files changed, 21 insertions(+), 6 deletions(-)
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index f3fa55b..3a74d91 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers)
wmb();
}
+static inline void virtio_store_mb(bool weak_barriers,
+ __virtio16 *p, __virtio16 v)
+{
+ if (weak_barriers)
+ virt_store_mb(*p, v);
+ else
+ {
The kernel coding style dictates:
if (weak_barriers) {
virt_store_mb(*p, v);
} else {
+ WRITE_ONCE(*p, v);
+ mb();
+ }
+}
+
[...]
MBR, Sergei
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