linux-kernel - Re: [PATCH] usbip: Fix the error limitation on max_hw

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Message-ID: <99a8b726-726a-4e26-bafc-9ff2b1e4d7be@linuxfoundation.org>
Date: Fri, 28 Mar 2025 15:14:31 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Zongmin Zhou <min_halo@....com>
Cc: valentina.manea.m@...il.com, shuah@...nel.org, i@...ithal.me,
 gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org, Zongmin Zhou <zhouzongmin@...inos.cn>,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] usbip: Fix the error limitation on max_hw_sectors for
 usbip device

On 3/13/25 04:02, Zongmin Zhou wrote:
> 
> On 2025/3/11 00:49, Shuah Khan wrote:
>> On 3/5/25 03:03, Zongmin Zhou wrote:
>>> At 2025-03-05 03:45:28, "Shuah Khan" <skhan@...uxfoundation.org> wrote:
>>>
>>>> On 3/2/25 05:37, Zongmin Zhou wrote:
>>>>> Dear shuah,
>>>>>
>>>>>
>>>>> Yes, I agree with you.It would be better if there have a more simpler fixes than This patch.
>>>>>
>>>>> I can just think of the two possible solutions that mentioned before.
>>>>
>>>  >What are the two possible solutions?
>>> 1. The patch we are discussing now,have to change the API between the kernel and user-space.
>>
>> 2. Simply set vhci-hcd dma mask to 64 by default,just modify the vhci-hcd driver. Then dma_max_mapping_size() will always return SIZE_MAX.
>>
>> I prefer option #2 - What are the downsides if any with this option?
>>
> If set vhci-hcd dma mask to 64 by default,I can't predict what will happen when the real USB controller support less than 64bit?
> 
> After all, the data flows from vhci-hcd to usbip-host and finally to the USB controller to which the device is actually connected.
> 
> the data is ultimately processed through the real USB controller?

Sorry for the delay.

That is the case. I have to check the code to see what the host
would do if it receives larger buffers from the client (vhci)
> 
> However, the default setting to 64-bit is equivalent to eliminating the impact of
> 
> the patch(commit d74ffae8b8dd) on usbip protocol devices, sounds feasible?
> 
> I am not very professional in this field, waiting for your evaluation.

We can give this a try. Send me the patch with default testing the
following cases:

Host - swiotlb enabled and disabled in your environment to see what
happens when there is a mismatch swiotlb enabled case and client
side doesn't limit the size.

thanks,
-- Shuah