Christopher, It sounds like you disabled zero-copy entirely, which is not necessary. As far as I recall, loading kernel modules is the only case in which valloc() allocated buffers are used. In the worst case, we only need to disable zero-copy on such buffers. I have been using a small patch to do precisely that since yesterday. I have attached it to this email since it sounds like the first version might be helpful to others while I take the time to explore a few loose ends. That being said, I would like to investigate a couple of things before I send either this patch or some variant of it to the appropriate subsystem maintainer. First, I need to review the valloc() routines to ensure that range checking against [VMALLOC_START, VMALLOC_END) is the correct way to identify valloc() generated buffers. Second, I want to explore the feasibility of a suggestion by Alexander Graf to instead rework the zero-copy to properly handle valloc() allocated buffers. Yours truly, Richard Yao On 11/26/2013 10:16 AM, Christopher Covington wrote: > Hi Richard, > > On 11/25/2013 04:50 PM, Richard Yao wrote: >> I figured out the problem. There is zerocopy IO is being done via DMA to >> a buffer allocated with valloc(). Right now, I am running a hack-fix >> locally so I can get some other stuff done first. I will propose a >> proper fix to the list in a few days. > > I've also encountered this issue on a non-QEMU simulator and have been > carrying a disable-zero-copy hack for a few months. Let me know if there's > anything I can help with. > > Christopher >
diff --git a/net/9p/client.c b/net/9p/client.c
index ee8fd6b..0adfcf5 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1557,7 +1557,9 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
rsize = count;
/* Don't bother zerocopy for small IO (< 1024) */
- if (clnt->trans_mod->zc_request && rsize > 1024) {
+ if (clnt->trans_mod->zc_request && rsize > 1024 &&
+ !(udata >= (char __user *)VMALLOC_START &&
+ udata < (char __user *)VMALLOC_END)) {
char *indata;
if (data) {
kernel_buf = 1;
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