From: Xianting Tian <xianting.tian@linux.alibaba.com>
To: Jiri Slaby <jirislaby@kernel.org>,
gregkh@linuxfoundation.org, amit@kernel.org, arnd@arndb.de
Cc: osandov@fb.com, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 2/2] virtio-console: remove unnecessary kmemdup()
Date: Mon, 2 Aug 2021 16:32:30 +0800 [thread overview]
Message-ID: <5ad81a0e-fbb2-a849-6db7-f5718633d282@linux.alibaba.com> (raw)
In-Reply-To: <b5554967-a683-96ae-deb9-2d4980d33b41@kernel.org>
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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:
>> 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 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.
>
>> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>> ---
>> 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);
>> }
>> /*
>>
>
>
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next prev parent reply other threads:[~2021-08-02 23:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-01 5:16 [PATCH 2/2] virtio-console: remove unnecessary kmemdup() Xianting Tian
2021-08-02 7:25 ` Jiri Slaby
2021-08-02 8:32 ` Xianting Tian [this message]
2021-08-02 8:40 ` Jiri Slaby
2021-08-02 8:55 ` Xianting Tian
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