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

hvc framework will never pass stack memory to the put_chars() function,
So the calling of kmemdup() is unnecessary, remove it.

Fixes: c4baad5029 ("virtio-console: avoid DMA from stack")
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);
 }
 
 /*

-- 
2.17.1

Hi,

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

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

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.

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.

-- 
js
suse labs

On 02. 08. 21, 10:32, Xianting Tian wrote:

在 2021/8/2 下午3:25, Jiri Slaby 写道:

quoted

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>

Oh, I did, but it's not properly threaded. PLease fix your setup.

quoted

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>

So is this a v2? You should have noted that. And what changed from v1 too.

quoted

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.

I don't see any input from the author?


Anyway, 1/2 does not even build, so you will send v3 with all the above 
fixed, hopefully.

thanks,
-- 
js

在 2021/8/2 下午4:40, Jiri Slaby 写道:

On 02. 08. 21, 10:32, Xianting Tian wrote:

quoted

在 2021/8/2 下午3:25, Jiri Slaby 写道:

quoted

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>

Oh, I did, but it's not properly threaded. PLease fix your setup.

Ok, thanks

quoted

quoted

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>

So is this a v2? You should have noted that. And what changed from v1 
too.

I think yes, I should mentioned it in this patch, sorry for that:(

quoted

quoted

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.

I don't see any input from the author?


Anyway, 1/2 does not even build, so you will send v3 with all the 
above fixed, hopefully.

yes, I will send v3 patch after I figured out a better solution based on 
Arnd's comments for the patch '1/2'.

Do you have any other suggestion for the solution?

thanks.

thanks,

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);
  }
    /*