Re: [PATCH V2 09/20] accel/amdxdna: Add context switch hysteresis with debugfs control

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] amdxdna: unaligned memory access in aie4_set_runtime_cfg()
--

commit 1c7fe2fcd8c5df7169f8d7c14de7898318de0123
Author: David Zhang <yidong.zhang@amd.com>

accel/amdxdna: Add context switch hysteresis with debugfs control

This commit adds aie4_set_ctx_hysteresis() to configure the AIE4 context
switch hysteresis timeout. It also exposes a debugfs node to change the
timeout at runtime.

> diff --git a/drivers/accel/amdxdna/aie4_message.c b/drivers/accel/amdxdna/aie4_message.c
> index 7112b0bc3725a..5720aa88e6d6d 100644
> --- a/drivers/accel/amdxdna/aie4_message.c
> +++ b/drivers/accel/amdxdna/aie4_message.c
[ ... ]
> @@ -262,3 +262,46 @@ int aie4_msg_set_power_mode(struct amdxdna_dev_hdl *ndev, u8 power_mode)
>  
>  	return ret;
>  }
> +
> +int aie4_set_runtime_cfg(struct amdxdna_dev_hdl *ndev, u32 type,
> +			 const void *data, size_t size)
> +{
> +	DECLARE_AIE_MSG(aie4_msg_set_runtime_cfg, AIE4_MSG_OP_SET_RUNTIME_CONFIG);
> +	u8 buf[sizeof(req.type) + AIE4_RUNTIME_CFG_MAX_DATA_SIZE] = { 0 };

[Severity: Medium]
Could this lead to unaligned memory access? The payload buffer is declared as
a byte array with no alignment guarantees, meaning its start address on the
stack might not be 4-byte aligned.

Later in this function, buf is assigned to msg.send_data and passed to
aie_send_mgmt_msg_wait(). When the mailbox code processes this message, it
does:

drivers/accel/amdxdna/amdxdna_mailbox.c:xdna_mailbox_send_msg() {
    ...
    if (unlikely(((u32 *)msg->send_data)[0] == TOMBSTONE)) {
    ...
}

Dereferencing a potentially unaligned pointer via a u32 pointer cast is
undefined behavior. While x86_64 hardware typically handles unaligned reads
gracefully, the compiler is permitted to optimize assuming the pointer is
strictly 4-byte aligned, which can lead to miscompilation. Furthermore, this
will trigger Undefined Behavior Sanitizer (UBSAN) warnings during runtime
testing.

Could the buffer be aligned, perhaps by using __aligned(4) or an appropriately
typed struct?

> +	int ret;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261006042230.547807-1-yidong.zhang@amd.com?part=9