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

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Message-ID: <61a6d459-338b-7e77-c78e-3a069bbfd690@linux.alibaba.com>
Date:   Mon, 2 Aug 2021 16:55:53 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     Jiri Slaby <jirislaby@...nel.org>, gregkh@...uxfoundation.org,
        amit@...nel.org, arnd@...db.de
Cc:     linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, osandov@...com
Subject: Re: [PATCH 2/2] virtio-console: remove unnecessary kmemdup()


在 2021/8/2 下午4:40, Jiri Slaby 写道:
> On 02. 08. 21, 10:32, Xianting Tian wrote:
>>
>> 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>
>
> Oh, I did, but it's not properly threaded. PLease fix your setup.
Ok, thanks
>
>>> 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 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:(

>
>>>> 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,