Re: [PATCH v1 1/4] misc: fastrpc: Add CRC support using invokeV2 request

Ekansh Gupta
2025-01-23T12:04:12Z

On 1/23/2025 4:43 PM, Dmitry Baryshkov wrote:
> On Thu, Jan 23, 2025 at 03:19:21PM +0530, Ekansh Gupta wrote:
>>
>>
>> On 1/23/2025 1:18 PM, Dmitry Baryshkov wrote:
>>> On Thu, Jan 23, 2025 at 11:16:41AM +0530, Ekansh Gupta wrote:
>>>>
>>>> On 10/7/2024 7:27 PM, Dmitry Baryshkov wrote:
>>>>> On Mon, Oct 07, 2024 at 02:15:15PM GMT, Ekansh Gupta wrote:
>>>>>> InvokeV2 request is intended to support multiple enhanced invoke
>>>>>> requests like CRC check, performance counter enablement and polling
>>>>>> mode for RPC invocations. CRC check is getting enabled as part of
>>>>>> this patch. CRC check for input and output argument helps in ensuring
>>>>>> data consistency over a remote call. If user intends to enable CRC
>>>>>> check, first local user CRC is calculated at user end and a CRC buffer
>>>>>> is passed to DSP to capture remote CRC values. DSP is expected to
>>>>>> write to the remote CRC buffer which is then compared at user level
>>>>>> with the local CRC values.
>>>>> This doesn't explain why this is necessary. Why do you need to checksum
>>>>> arguments?
>>>> This helps if the user suspects any data inconsistencies in the buffers passed to DSP over
>>>> remote call. This is not enabled by default and user can enable it as per their reqirement.
>>>> I'll add this information.
>>> An inconsistency where? Between the kernel and the DSP? Between the user
>>> and the DSP? Does it cover buffer contents or just the addresses?
>> Inconsistency between user and DSP. crc_user is calculated at user library before
>> making ioctl call and it is compared against the crc data which is filled by DSP and
>> copied to user.
>> This covers inconsistency in buffer contents.
> What is the reason for possible inconsistencies? Is it a debugging
> feature?
This is a debugging feature. Buffer data corruption might result in inconsistency.
>
>>>>> Also, what if the DSP firmware doesn't support CRC? How should userspace
>>>>> know that?
>>>> CRC support on DSP is there since long time(>6years).
>>> This doesn't give us a lot. Upstream kernel supports fastrpc since
>>> MSM8916 and MSM8996. Do those platforms support CRC?
>> The metadata buffer as of today also carries space for CRC information:
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/misc/fastrpc.c#n877
>>
>> So this is common across all platforms.
>>
>> In case CRC is not supported on any older platform, it would result in crc mismatch at user library.
>> As of now a warning is getting logged there, I can add the information suggesting the failure might
>> also occur if CRC is not supported.
> Logs go to /dev/null, they are ignored by users, etc. So either there
> should be an actual error being returned by the kernel / library, or it
> can be completely ignored and skipped.
>
> So, do MSM8916 / MSM8996 / SDM845 support CRC? If not, that must be
> handled somehow.
I see it's supported on SDM845 but not on MSM89##. I'll just send the new patch version for now
as CRC mismatch failures are getting ignored.
>
>>> And if they do, why do we need the invoke_v2? Can we modify existing
>>> code instead?
>> invoke_v2 is needed because there is a need to pass user crc pointer over ioctl call which
>> cannot be achieved using existing code. Also there are plans to add more features to this
>> invoke_v2 request which will carry some information from user.
> Is it really extensible without breaking the ABI?
I'm planning to keep reserved bits in uapi struct for the same. Do you see any
problem with this?
>>>> From user space CRC check failure is
>>>> not fatal and is printed as a warning. But if copy of CRC to user fails, it will result in remote
>>>> call failure. Should I keep it as fatal considering that ever very old DSP support this or should
>>>> I consider the copy failure as non-fatal as userspace is treating this as a warning?
>>> warnings can remain unseen for a long time. Consider a GUI app. Nobody
>>> is there to view kernel warnings or library output.
>> Let me see if this can be done. Are you suggesting that the app will be somewhat tracking
>> if there is any crc check mismatch failures?
> I suggest returning -EIO to the app.
I'll check this.
>
>>>>>> Signed-off-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
>>>>>> ---
>>>>>> drivers/misc/fastrpc.c | 161 ++++++++++++++++++++++++------------
>>>>>> include/uapi/misc/fastrpc.h | 7 ++
>>>>>> 2 files changed, 116 insertions(+), 52 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>>>>>> index 74181b8c386b..8e817a763d1d 100644
>>>>>> --- a/drivers/misc/fastrpc.c
>>>>>> +++ b/drivers/misc/fastrpc.c
>>>>>> @@ -573,13 +573,15 @@ static void fastrpc_get_buff_overlaps(struct fastrpc_invoke_ctx *ctx)
>>>>>>
>>>>>> static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
>>>>>> struct fastrpc_user *user, u32 kernel, u32 sc,
>>>>>> - struct fastrpc_invoke_args *args)
>>>>>> + struct fastrpc_invoke_v2 *inv2)
>>>>>> {
>>>>>> struct fastrpc_channel_ctx *cctx = user->cctx;
>>>>>> struct fastrpc_invoke_ctx *ctx = NULL;
>>>>>> + struct fastrpc_invoke_args *args = NULL;
>>>>> Why do you need to init to NULL if you are going to set it two lines
>>>>> below?
>>>>>
>>>>>> unsigned long flags;
>>>>>> int ret;
>>>>>>
>>>>>> + args = (struct fastrpc_invoke_args *)inv2->inv.args;
>>>>> Why does it need a typecast?
>>>>>
>>>>>> ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>>>>>> if (!ctx)
>>>>>> return ERR_PTR(-ENOMEM);
>>>>>> @@ -611,6 +613,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
>>>>>> /* Released in fastrpc_context_put() */
>>>>>> fastrpc_channel_ctx_get(cctx);
>>>>>>
>>>>>> + ctx->crc = (u32 *)(uintptr_t)inv2->crc;
>>>>> Oh, but why? Also is it a user pointer or in-kernel data? If it's a
>>>>> user-based pointer, where is the accessiblity check? Why isn't it
>>>>> annotated properly?
>>>> This is a user pointer where the crc data is expected to be copied. There is no
>>>> other access to this pointer from kernel. I'm planning to change the data type
>>>> for crc as (void __user*) inside fastrpc_invoke_ctx structure.
>>> Yes, please. Also make sure that sparse doesn't add any warnings
>>> regarding pointer conversions.
>> Ack.
>>>>>> ctx->sc = sc;
>>>>>> ctx->retval = -1;
>>>>>> ctx->pid = current->pid;
>>>>>> @@ -1070,6 +1073,7 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx,
>>>>>> struct fastrpc_invoke_buf *list;
>>>>>> struct fastrpc_phy_page *pages;
>>>>>> u64 *fdlist;
>>>>>> + u32 *crclist;
>>>>>> int i, inbufs, outbufs, handles;
>>>>>>
>>>>>> inbufs = REMOTE_SCALARS_INBUFS(ctx->sc);
>>>>>> @@ -1078,6 +1082,7 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx,
>>>>>> list = fastrpc_invoke_buf_start(rpra, ctx->nscalars);
>>>>>> pages = fastrpc_phy_page_start(list, ctx->nscalars);
>>>>>> fdlist = (uint64_t *)(pages + inbufs + outbufs + handles);
>>>>>> + crclist = (u32 *)(fdlist + FASTRPC_MAX_FDLIST);
>>>>> I think we should rewrite this parsing somehow. Is the format of data
>>>>> documented somewhere?
>>>> fdlist, crclist and poll(planned) are the only pointers that is being used. I'm planning
>>>> to store these pointers to ctx structure and directly use it wherever needed. This will
>>>> clean-up this unnecessary calculations at multiple places.
>>> Please do. Nevertheless, the format also must be documented.
>> Ack.
>>>>>>
>>>>>> for (i = inbufs; i < ctx->nbufs; ++i) {
>>>>>> if (!ctx->maps[i]) {
>>>>>> @@ -1102,6 +1107,12 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx,
>>>>>> fastrpc_map_put(mmap);
>>>>>> }
>>>>>>
>>>>>> + if (ctx->crc && crclist && rpra) {
>>>>>> + if (copy_to_user((void __user *)ctx->crc, crclist,
>>>>>> + FASTRPC_MAX_CRCLIST * sizeof(u32)))
>>>>> Oh, so it's a user pointer. Then u32* was completely incorrect.
>>>>> Also you are copying FASTRPC_MAX_CRCLIST elements. Are all of them
>>>>> filled? Or are we leaking some data to userspace?
>>>> Yes, right. Planning clean-up in next patch.
>>>>
>>>> All of FASTRPC_MAX_CRCLIST is filled with crc data by DSP so copying should be fine.
>>> Huh? I definitely want to see documentation for function arguments.
>> Sure. I'll also modify the metadata layout doc here to add fdlist, CRC and other planned contents.
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/misc/fastrpc.c#n842
> This is not a documentation. E.g. I can not write code using that
> description. For example, it mentions neither FDLIST nor CRC.
I'm planning to add complete documentation for CRC and polling mode in user library project.
If I need to add documentation in driver, can you pls suggest what is the right place to add
the information?

Thanks for your comments.

--ekansh
>
>>>>>> + return -EFAULT;
>>>>>> + }
>>>>>> +
>>>>>> return 0;
>>>>>> }
>>>>>>