linux-kernel - Re: [PATCH v1 2/3] misc: fastrpc: Free DMA handles for RPC calls with no arguments

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Message-ID: <856929f7-7e6e-8dd5-a12f-9f4de524ce61@quicinc.com>
Date:   Tue, 3 Oct 2023 16:37:30 +0530
From:   Ekansh Gupta <quic_ekangupt@...cinc.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        <linux-arm-msm@...r.kernel.org>
CC:     <ekangupt@....qualcomm.com>, <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>,
        <fastrpc.upstream@....qualcomm.com>, stable <stable@...nel.org>
Subject: Re: [PATCH v1 2/3] misc: fastrpc: Free DMA handles for RPC calls with
 no arguments



On 10/2/2023 3:00 PM, Srinivas Kandagatla wrote:
> 
> 
> On 29/09/2023 08:42, Ekansh Gupta wrote:
>> The FDs for DMA handles to be freed is updated in fdlist by DSP over
>> a remote call. This holds true even for remote calls with no
>> arguments. To handle this, get_args and put_args are needed to
>> be called for remote calls with no arguments also as fdlist
>> is allocated in get_args and FDs updated in fdlist is freed
>> in put_args.
>>
>> Fixes: 8f6c1d8c4f0c ("misc: fastrpc: Add fdlist implementation")
>> Cc: stable <stable@...nel.org>
>> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
>> ---
>>   drivers/misc/fastrpc.c | 23 ++++++++++-------------
>>   1 file changed, 10 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index fb92197..a52701c 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -1091,6 +1091,7 @@ static int fastrpc_put_args(struct 
>> fastrpc_invoke_ctx *ctx,
>>           }
>>       }
>> +    /* Clean up fdlist which is updated by DSP */
>>       for (i = 0; i < FASTRPC_MAX_FDLIST; i++) {
>>           if (!fdlist[i])
>>               break;
>> @@ -1157,11 +1158,9 @@ static int fastrpc_internal_invoke(struct 
>> fastrpc_user *fl,  u32 kernel,
>>       if (IS_ERR(ctx))
>>           return PTR_ERR(ctx);
> <---
>> -    if (ctx->nscalars) {
>> -        err = fastrpc_get_args(kernel, ctx);
>> -        if (err)
>> -            goto bail;
>> -    }
>> +    err = fastrpc_get_args(kernel, ctx);
>> +    if (err)
>> +        goto bail;
> -->
> I dont see any point of the above change as fastrpc_internal_invoke will 
> be called from kernel with nscalars always set.
> 
> do you see a path that does not set this?
> 
The context specific rpra buffer is allocated as part of 
fastrpc_get_args and there is a possibility that the DSP intends to 
update fdlist for a call with 0 nscalars. In that scenario, the driver 
needs to ensure that the rpra is allocated which will carry the fdlist. 
The same can be extended to crc and dsp perf memory(to be added, patches 
shared for missing features) for remote calls with 0 nscalars.

Thanks for taking your time to review the patches Srini, please let me 
know if you have more queries.

-ekansh
> --srini
>>       /* make sure that all CPU memory writes are seen by DSP */
>>       dma_wmb();
>> @@ -1185,14 +1184,12 @@ static int fastrpc_internal_invoke(struct 
>> fastrpc_user *fl,  u32 kernel,
>>       if (err)
>>           goto bail;
>> -    if (ctx->nscalars) {
>> -        /* make sure that all memory writes by DSP are seen by CPU */
>> -        dma_rmb();
>> -        /* populate all the output buffers with results */
>> -        err = fastrpc_put_args(ctx, kernel);
>> -        if (err)
>> -            goto bail;
>> -    }
>> +    /* make sure that all memory writes by DSP are seen by CPU */
>> +    dma_rmb();
>> +    /* populate all the output buffers with results */
>> +    err = fastrpc_put_args(ctx, kernel);
>> +    if (err)
>> +        goto bail;
>>   bail:
>>       if (err != -ERESTARTSYS && err != -ETIMEDOUT) {