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Date:   Thu, 4 Aug 2022 13:22:49 +0000
From:   <Ajay.Kathat@...rochip.com>
To:     <michael@...le.cc>
CC:     <David.Laight@...lab.com>, <Claudiu.Beznea@...rochip.com>,
        <kvalo@...nel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>,
        <linux-wireless@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <mwalle@...nel.org>
Subject: Re: [PATCH] wilc1000: fix DMA on stack objects

On 04/08/22 18:26, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
> the content is safe
>
> Am 2022-08-04 14:43, schrieb Ajay.Kathat@...rochip.com:
>> On 04/08/22 12:52, Michael Walle wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know
>>> the content is safe
>>>
>>> Am 2022-07-29 17:39, schrieb Ajay.Kathat@...rochip.com:
>>>> On 29/07/22 20:28, Michael Walle wrote:
>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you
>>>>> know
>>>>> the content is safe
>>>>>
>>>>> Am 29. Juli 2022 11:51:12 MESZ schrieb David Laight
>>>>> <David.Laight@...LAB.COM>:
>>>>>> From: Michael Walle
>>>>>>> Sent: 28 July 2022 16:21
>>>>>>>
>>>>>>> From: Michael Walle <mwalle@...nel.org>
>>>>>>>
>>>>>>> Sometimes wilc_sdio_cmd53() is called with addresses pointing to
>>>>>>> an
>>>>>>> object on the stack. E.g. wilc_sdio_write_reg() will call it with
>>>>>>> an
>>>>>>> address pointing to one of its arguments. Detect whether the
>>>>>>> buffer
>>>>>>> address is not DMA-able in which case a bounce buffer is used. The
>>>>>>> bounce
>>>>>>> buffer itself is protected from parallel accesses by
>>>>>>> sdio_claim_host().
>>>>>>>
>>>>>>> Fixes: 5625f965d764 ("wilc1000: move wilc driver out of staging")
>>>>>>> Signed-off-by: Michael Walle <mwalle@...nel.org>
>>>>>>> ---
>>>>>>> The bug itself probably goes back way more, but I don't know if it
>>>>>>> makes
>>>>>>> any sense to use an older commit for the Fixes tag. If so, please
>>>>>>> suggest
>>>>>>> one.
>>>>>>>
>>>>>>> The bug leads to an actual error on an imx8mn SoC with 1GiB of
>>>>>>> RAM.
>>>>>>> But the
>>>>>>> error will also be catched by CONFIG_DEBUG_VIRTUAL:
>>>>>>> [    9.817512] virt_to_phys used for non-linear address:
>>>>>>> (____ptrval____) (0xffff80000a94bc9c)
>>>>>>>
>>>>>>>   .../net/wireless/microchip/wilc1000/sdio.c    | 28
>>>>>>> ++++++++++++++++---
>>>>>>>   1 file changed, 24 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>>>>> b/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>>>>> index 7962c11cfe84..e988bede880c 100644
>>>>>>> --- a/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>>>>> +++ b/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>>>>> @@ -27,6 +27,7 @@ struct wilc_sdio {
>>>>>>>       bool irq_gpio;
>>>>>>>       u32 block_size;
>>>>>>>       int has_thrpt_enh3;
>>>>>>> +    u8 *dma_buffer;
>>>>>>>   };
>>>>>>>
>>>>>>>   struct sdio_cmd52 {
>>>>>>> @@ -89,6 +90,9 @@ static int wilc_sdio_cmd52(struct wilc *wilc,
>>>>>>> struct sdio_cmd52 *cmd)
>>>>>>>   static int wilc_sdio_cmd53(struct wilc *wilc, struct sdio_cmd53
>>>>>>> *cmd)
>>>>>>>   {
>>>>>>>       struct sdio_func *func = container_of(wilc->dev, struct
>>>>>>> sdio_func, dev);
>>>>>>> +    struct wilc_sdio *sdio_priv = wilc->bus_data;
>>>>>>> +    bool need_bounce_buf = false;
>>>>>>> +    u8 *buf = cmd->buffer;
>>>>>>>       int size, ret;
>>>>>>>
>>>>>>>       sdio_claim_host(func);
>>>>>>> @@ -100,12 +104,20 @@ static int wilc_sdio_cmd53(struct wilc
>>>>>>> *wilc,
>>>>>>> struct sdio_cmd53 *cmd)
>>>>>>>       else
>>>>>>>               size = cmd->count;
>>>>>>>
>>>>>>> +    if ((!virt_addr_valid(buf) || object_is_on_stack(buf)) &&
>>>>>> How cheap are the above tests?
>>>>>> It might just be worth always doing the 'bounce'?
>>>>> I'm not sure how cheap they are, but I don't think it costs more
>>>>> than
>>>>> copying the bulk data around. That's up to the maintainer to decide.
>>>>
>>>>
>>>> I think, the above checks for each CMD53 might add up to the
>>>> processing
>>>> time of this function. These checks can be avoided, if we add new
>>>> function similar to 'wilc_sdio_cmd53' which can be called when the
>>>> local
>>>> variables are used. Though we have to perform the memcpy operation
>>>> which
>>>> is anyway required to handle this scenario for small size data.
>>>>
>>>> Mostly, either the static global data or dynamically allocated buffer
>>>> is
>>>> used with cmd53 except wilc_sdio_write_reg, wilc_sdio_read_reg
>>>> wilc_wlan_handle_txq functions.
>>>>
>>>> I have created a patch using the above approach which can fix this
>>>> issue
>>>> and will have no or minimal impact on existing functionality. The
>>>> same
>>>> is copied below:
>>>>
>>>>
>>>> ---
>>>>   .../net/wireless/microchip/wilc1000/netdev.h  |  1 +
>>>>   .../net/wireless/microchip/wilc1000/sdio.c    | 46
>>>> +++++++++++++++++--
>>>>   .../net/wireless/microchip/wilc1000/wlan.c    |  2 +-
>>>>   3 files changed, 45 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/net/wireless/microchip/wilc1000/netdev.h
>>>> b/drivers/net/wireless/microchip/wilc1000/netdev.h
>>>> index 43c085c74b7a..2137ef294953 100644
>>>> --- a/drivers/net/wireless/microchip/wilc1000/netdev.h
>>>> +++ b/drivers/net/wireless/microchip/wilc1000/netdev.h
>>>> @@ -245,6 +245,7 @@ struct wilc {
>>>>       u8 *rx_buffer;
>>>>       u32 rx_buffer_offset;
>>>>       u8 *tx_buffer;
>>>> +    u32 vmm_table[WILC_VMM_TBL_SIZE];
>>>>
>>>>       struct txq_handle txq[NQUEUES];
>>>>       int txq_entries;
>>>> diff --git a/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>> b/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>> index 600cc57e9da2..19d4350ecc22 100644
>>>> --- a/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>> +++ b/drivers/net/wireless/microchip/wilc1000/sdio.c
>>>> @@ -28,6 +28,7 @@ struct wilc_sdio {
>>>>       u32 block_size;
>>>>       bool isinit;
>>>>       int has_thrpt_enh3;
>>>> +    u8 *dma_buffer;
>>>>   };
>>>>
>>>>   struct sdio_cmd52 {
>>>> @@ -117,6 +118,36 @@ static int wilc_sdio_cmd53(struct wilc *wilc,
>>>> struct sdio_cmd53 *cmd)
>>>>       return ret;
>>>>   }
>>>>
>>>> +static int wilc_sdio_cmd53_extend(struct wilc *wilc, struct
>>>> sdio_cmd53
>>>> *cmd)
>>>
>>> If you handle all the stack cases anyway, the caller can just use
>>> a bounce buffer and you don't need to duplicate the function.
>>
>>
>> Thanks. Indeed, the duplicate function can be avoided. I will update
>> the
>> patch and send modified patch for the review.
>> Btw, I was trying to reproduce the warning message by enabling
>> CONFIG_DEBUG_VIRTUAL config but no luck. It seems enabling the config
>> is
>> not enough to test on my host or may be I am missing something.
>
> Did you bring the interface up?

Yes, I tested by bringing the interface up on SAMA5D4 Xplained host.

>
>> I would
>> need the help to test and confirm if the modified patch do solve the
>> issue with imx8mn.
>
> sure, just put me on cc and i can test it on my board. 

Sure. Thanks.


Regards,
Ajay

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