linux-kernel - Re: [PATCH] vhost: correctly set bits of dirty pages

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Date:	Mon, 29 Nov 2010 10:25:53 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	virtualization@...ts.osdl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] vhost: correctly set bits of dirty pages

On Mon, Nov 29, 2010 at 10:18:40AM +0200, Michael S. Tsirkin wrote:
> On Mon, Nov 29, 2010 at 01:48:20PM +0800, Jason Wang wrote:
> > When counting pages we should increase it by 1 instead of VHOST_PAGE_SIZE,
> > and also make log_write() can correctly process the request across
> > pages with write_address not start at page boundary.
> > 
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> 
> 
> Thanks, good catch!
> But let's to it in small steps: first, a small patch to fix the bug:
> I think this is equivalent, right?
> 
> Subject: vhost: correctly set bits of dirty pages
> 
> When counting pages we should increase address by 1 instead of
> VHOST_PAGE_SIZE, and also make log_write() can correctly process the
> request across pages with write_address not starting at page boundary.
> 
> Reported-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

And then this on top:


vhost: better variable name in logging

We really store a page offset in write_address,
so rename it write_page to avoid confusion.

Signed-off-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

---

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d0a3552..1a3d3ed 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -884,15 +884,15 @@ static int set_bit_to_user(int nr, void __user *addr)
 static int log_write(void __user *log_base,
 		     u64 write_address, u64 write_length)
 {
+	u64 write_page = write_address / VHOST_PAGE_SIZE
 	int r;
 	if (!write_length)
 		return 0;
 	write_length += write_address % VHOST_PAGE_SIZE;
-	write_address /= VHOST_PAGE_SIZE;
 	for (;;) {
 		u64 base = (u64)(unsigned long)log_base;
-		u64 log = base + write_address / 8;
-		int bit = write_address % 8;
+		u64 log = base + write_page / 8;
+		int bit = write_page % 8;
 		if ((u64)(unsigned long)log != log)
 			return -EFAULT;
 		r = set_bit_to_user(bit, (void __user *)(unsigned long)log);
@@ -901,7 +901,7 @@ static int log_write(void __user *log_base,
 		if (write_length <= VHOST_PAGE_SIZE)
 			break;
 		write_length -= VHOST_PAGE_SIZE;
-		write_address += 1;
+		write_page += 1;
 	}
 	return r;
 }
--
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