Re: [PATCH 2/2] virtio-console: remove unnecessary kmemdup()

在 2021/8/2 下午3:25, Jiri Slaby 写道:

Hi,

why is this 2/2? I seem (Lore neither) to find 1/2.

You didn't receive 1/2?
[PATCH 1/2] tty: hvc: pass DMA capable memory to put_chars()
https://lkml.org/lkml/2021/8/1/8 <https://lkml.org/lkml/2021/8/1/8>

On 01. 08. 21, 7:16, Xianting Tian wrote:

quoted

hvc framework will never pass stack memory to the put_chars() function,

Am I blind or missing something?

hvc_console_print(...)
{
  char c[N_OUTBUF]
...
  cons_ops[index]->put_chars(vtermnos[index], c, i);

The same here:

hvc_poll_put_char(..., char ch)
{
...
   n = hp->ops->put_chars(hp->vtermno, &ch, 1);

AFAICS both of them *pass* a pointer to stack variable.

yes, I discussed the issue with Arnd before in below thread,  you can 
get the history, thanks

https://lkml.org/lkml/2021/7/27/494 <https://lkml.org/lkml/2021/7/27/494>

quoted

So the calling of kmemdup() is unnecessary, remove it.

Fixes: c4baad5029 ("virtio-console: avoid DMA from stack")

This patch doesn't "Fix" -- it reverts the commit. You should've CCed 
the author too.

yes, we discussed ther issue in above thread, which we CCed the author.

quoted

Signed-off-by: Xianting Tian <redacted>
---
  drivers/char/virtio_console.c | 12 ++----------
  1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/drivers/char/virtio_console.c 

b/drivers/char/virtio_console.c
index 7eaf303a7..4ed3ffb1d 100644

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c

@@ -1117,8 +1117,6 @@ static int put_chars(u32 vtermno, const char 

*buf, int count)
  {
      struct port *port;
      struct scatterlist sg[1];
-    void *data;
-    int ret;
        if (unlikely(early_put_chars))
          return early_put_chars(vtermno, buf, count);

@@ -1127,14 +1125,8 @@ static int put_chars(u32 vtermno, const char 

*buf, int count)
      if (!port)
          return -EPIPE;
  -    data = kmemdup(buf, count, GFP_ATOMIC);
-    if (!data)
-        return -ENOMEM;
-
-    sg_init_one(sg, data, count);
-    ret = __send_to_port(port, sg, 1, count, data, false);
-    kfree(data);
-    return ret;
+    sg_init_one(sg, buf, count);
+    return __send_to_port(port, sg, 1, count, (void *)buf, false);
  }
    /*