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* [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers
@ 2013-12-04 20:43 Richard Yao
  2013-12-04 20:49 ` Alexander Graf
  2013-12-06 11:14 ` Will Deacon
  0 siblings, 2 replies; 10+ messages in thread
From: Richard Yao @ 2013-12-04 20:43 UTC (permalink / raw)
  To: virtualization
  Cc: Eric Van Hensbergen, Will Deacon, kernel, Aneesh Kumar K.V,
	Ron Minnich, v9fs-developer, Brian Behlendorf

The 9p-virtio transport does zero copy on things larger than 1024 bytes
in size. It accomplishes this by returning the physical addresses of
pages to the virtio-pci device. At present, the translation is usually a
bit shift.

However, that approach produces an invalid page address when we
read/write to vmalloc buffers, such as those used for Linux kernle
modules. This causes QEMU to die printing:

qemu-system-x86_64: virtio: trying to map MMIO memory

This patch enables 9p-virtio to correctly handle this case. This not
only enables us to load Linux kernel modules off virtfs, but also
enables ZFS file-based vdevs on virtfs to be used without killing QEMU.

Also, special thanks to both Avi Kivity and Alexander Graf for their
interpretation of QEMU backtraces. Without their guidence, tracking down
this bug would have taken much longer.

Signed-off-by: Richard Yao <ryao@gentoo.org>
---
 net/9p/trans_virtio.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 9c5a1aa..5d1d04b 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -340,7 +340,10 @@ static int p9_get_mapped_pages(struct virtio_chan *chan,
 		int count = nr_pages;
 		while (nr_pages) {
 			s = rest_of_page(data);
-			pages[index++] = kmap_to_page(data);
+			if (is_vmalloc_or_module_addr(data))
+				pages[index++] = vmalloc_to_page(data);
+			else
+				pages[index++] = kmap_to_page(data);
 			data += s;
 			nr_pages--;
 		}
-- 
1.8.3.2

^ permalink raw reply related	[flat|nested] 10+ messages in thread
* [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers (second submission)
@ 2014-01-30 18:02 Richard Yao
  2014-01-30 18:02 ` [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Richard Yao
  0 siblings, 1 reply; 10+ messages in thread
From: Richard Yao @ 2014-01-30 18:02 UTC (permalink / raw)
  To: Eric Van Hensbergen
  Cc: Ron Minnich, Latchesar Ionkov, David S. Miller,
	V9FS Develooper Mailing List, Linux Netdev Mailing List,
	Linux Kernel Mailing List, Gentoo Kernel Team, Aneesh Kumar K.V,
	Will Deacon, Christopher Covington, Brian Behlendorf,
	Matthew Thode, Richard Yao

This is my first real patch submission, which I sent out in December.
Unfortunately, I sent it to only a subset of the correct people. Time passed,
Greg Koah-Hartman was kind enough to give me some pointers and I am now sending
it back out to the correct people. My apologies to anyone who was bit by this
issue because it was not sent to the correct people sooner.

Richard Yao (1):
  9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers

 net/9p/trans_virtio.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
1.8.3.2


^ permalink raw reply	[flat|nested] 10+ messages in thread
* [PATCH] Fix broken zero-copy on vmalloc() buffers (4th and hopefully final submission)
@ 2014-02-09  0:32 Richard Yao
  2014-02-09  0:32 ` [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Richard Yao
  0 siblings, 1 reply; 10+ messages in thread
From: Richard Yao @ 2014-02-09  0:32 UTC (permalink / raw)
  To: David S. Miller
  Cc: Eric Van Hensbergen, Ron Minnich, Latchesar Ionkov,
	V9FS Develooper Mailing List, Linux Netdev Mailing List,
	Linux Kernel Mailing List, Aneesh Kumar K.V, Will Deacon,
	Christopher Covington, Matthew Thode

This patch has been submitted for a few times.

The first time was my first time doing any sort of Linux patch
submission. At the time, I was unaware of ./scripts/get_maintainer.pl
and sent the patch to only a subset of the correct people. Consequently,
it was not submitted properly for acceptance by the subsystem maintainer.

The second time was a week ago. I had taken advice from Greg Koah-Hartman to
use ./scripts/get_maintainer.pl to determine the correct recipients. It was
initially accepted by the subsystem maintainer and then rejected. This patch
uses is_vmalloc_or_module_addr(), which is not exported for use in kernel
modules. Using it causes a build failure when CONFIG_NET_9P_VIRTIO=m is set in
.config.

The third time was earlier today, when I sent it straight to Linus Torvalds
because merging it required exporting is_vmalloc_or_module_addr(), which he
wrote. A brief correspondence with Linus revealed that my earlier belief that
it would be better to use is_vmalloc_or_module_addr() instead of
is_vmalloc_addr() was incorrect.

I expect this submission to be the last. I have changed the patch to use
is_vmalloc_addr() as Linus Torvalds suggested. This resolves the build
regression the problem David S. Miller found when CONFIG_NET_9P_VIRTIO=m was
set and should resolve all criticism.

Richard Yao (1):
  9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers

 net/9p/trans_virtio.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
1.8.3.2


^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2014-02-09  0:32 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-12-04 20:43 [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Richard Yao
2013-12-04 20:49 ` Alexander Graf
2013-12-06 11:14 ` Will Deacon
2013-12-06 14:38   ` Richard Yao
2013-12-06 16:29     ` Will Deacon
  -- strict thread matches above, loose matches on Subject: below --
2014-01-30 18:02 [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers (second submission) Richard Yao
2014-01-30 18:02 ` [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Richard Yao
2014-01-31  0:29   ` David Miller
2014-01-31  0:44     ` David Miller
2014-01-31  1:02       ` Richard Yao
2014-02-09  0:32 [PATCH] Fix broken zero-copy on vmalloc() buffers (4th and hopefully final submission) Richard Yao
2014-02-09  0:32 ` [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Richard Yao

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