Re: [PATCH v10 RESEND 3/9] riscv: sse: mask events during shutdown and kexec

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] riscv: dead code in UP panic_smp_self_stop() misses early SSE mask
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commit 7602c0f047088ef36df958ced3408ede048d0ce9
Author: Zhanpeng Zhang <zhangzhanpeng.jasper@bytedance.com>

riscv: sse: mask events during shutdown and kexec

This commit masks SSE events on the local hart before panic stop, CPU stop,
restart, poweroff, and crash shutdown paths to prevent firmware from entering
a Linux-owned handler state after the CPU or kernel context becomes invalid.
It also rejects normal kexec from a crash kernel to avoid transferring unknown
firmware state to the new kernel.

> diff --git a/arch/riscv/kernel/reset.c b/arch/riscv/kernel/reset.c
> index 14eb08a6db855..fdab37e7ae52d 100644
> --- a/arch/riscv/kernel/reset.c
> +++ b/arch/riscv/kernel/reset.c
> @@ -6,6 +6,20 @@
>  #include <linux/efi.h>
>  #include <linux/reboot.h>
>  #include <linux/pm.h>
> +#include <linux/smp.h>
> +
> +#include <asm/sse.h>
> +
> +#ifndef CONFIG_SMP
> +void __noreturn panic_smp_self_stop(void)
> +{
> +	riscv_sse_mask_current_hart();
> +	local_irq_disable();
> +
> +	for (;;)
> +		cpu_relax();
> +}
> +#endif

[Severity: Low]
Is this panic_smp_self_stop() function reachable on UP systems?

When a kernel panic occurs on a UP system, the single CPU will always win the
panic_try_start() race and proceed as the primary panicking CPU. The primary
panicking CPU never calls panic_smp_self_stop().

Additionally, on UP systems, the smp_send_stop() and crash_smp_send_stop()
functions are inline no-ops, so the primary CPU does not mask its own SSE
early in the panic path. Although a follow-up patch (Patch 4) adds a panic
notifier that eventually masks the SSE before the final infinite loop, the UP
CPU remains unmasked during the early panic stages (such as stack trace
dumping), and this added UP code appears to be entirely dead.

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1789974241.git.zhangzhanpeng.jasper@bytedance.com?part=3