linux-kernel - Re: [PATCH v5 2/2] misc: fastrpc: Increase unsigned PD initmem size

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Message-ID: <35e52822-a81f-4b2c-adc1-903785ce1849@quicinc.com>
Date: Mon, 22 Jul 2024 11:55:19 +0530
From: Ekansh Gupta <quic_ekangupt@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <srinivas.kandagatla@...aro.org>, <linux-arm-msm@...r.kernel.org>,
        <quic_bkumar@...cinc.com>, <linux-kernel@...r.kernel.org>,
        <quic_chennak@...cinc.com>, <dri-devel@...ts.freedesktop.org>,
        <arnd@...db.de>, stable <stable@...nel.org>
Subject: Re: [PATCH v5 2/2] misc: fastrpc: Increase unsigned PD initmem size



On 7/22/2024 11:30 AM, Greg KH wrote:
> On Mon, Jul 22, 2024 at 11:24:37AM +0530, Ekansh Gupta wrote:
>> For unsigned PD offloading requirement, additional memory is required
>> because of additional static heap initialization. Without this
>> additional memory, PD initialization would fail. Increase the initmem
>> size by 2MB for unsigned PD initmem buffer allocation. Any additional
>> memory sent to DSP during PD init is used as the PD heap.
>>
>> Fixes: 7f1f481263c3 ("misc: fastrpc: check before loading process to the DSP")
>> Cc: stable <stable@...nel.org>
>> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
>> ---
>>  drivers/misc/fastrpc.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index a3a5b745936e..18668b020a87 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -40,6 +40,7 @@
>>  #define FASTRPC_CTXID_MASK (0xFF0)
>>  #define INIT_FILELEN_MAX (2 * 1024 * 1024)
>>  #define FASTRPC_INITLEN_MIN (3 * 1024 * 1024)
>> +#define FASTRPC_STATIC_HEAP_LEN (2 * 1024 * 1024)
>>  #define INIT_FILE_NAMELEN_MAX (128)
>>  #define FASTRPC_DEVICE_NAME	"fastrpc"
>>  
>> @@ -1411,8 +1412,14 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
>>  			goto err;
>>  	}
>>  
>> +	/* Allocate buffer in kernel for donating to remote process.
>> +	 * Unsigned PD requires additional memory because of the
> What is "PD"?
DSP PD(protection domain) is execution environment supported by DSP.
>
>> +	 * additional static heap initialized within the process.
>> +	 */
> Why are you using networking comment style for a non-networking file?
I observed similar style in this driver file. I will update this in proper style in the next patch.
>
>>  	memlen = ALIGN(max(FASTRPC_INITLEN_MIN, (int)init.filelen * 4),
>>  		       1024 * 1024);
>> +	if (unsigned_module)
>> +		memlen += FASTRPC_STATIC_HEAP_LEN;
> I don't understand, why is "static heap length" being added for
> something that is "unsigned"?  Why isn't this just "SIGNING FREE SPACE"
> or something like that?
The difference between signed PD and unsigned PD is:
Signed PD: Available on all DSPs and requires that the shared objects being loaded in the PD
are signed with a digital signature.

Unsigned PD: Sandboxed low-rights process that allows signature-free shared objects to run on
CDSP.

For unsigned PD there are some additional statically initialized heap for which additional memory
is required. I'll try to come up with a better name.

Thanks for the review.

--Ekansh
>
> thanks,
>
> greg "naming is hard" k-h
>