[PATCH] riscv: Flush current cpu icache before other cpus

[Palmer Dabbelt]

On Sat, 18 Sep 2021 09:02:21 PDT (-0700), alex at ghiti.fr wrote:
> On SiFive Unmatched, I recently fell onto the following BUG when booting:
>
> [    0.000000] ftrace: allocating 36610 entries in 144 pages
> [    0.000000] Oops - illegal instruction [#1]
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.13.1+ #5
> [    0.000000] Hardware name: SiFive HiFive Unmatched A00 (DT)
> [    0.000000] epc : riscv_cpuid_to_hartid_mask+0x6/0xae
> [    0.000000]  ra : __sbi_rfence_v02+0xc8/0x10a
> [    0.000000] epc : ffffffff80007240 ra : ffffffff80009964 sp : ffffffff81803e10
> [    0.000000]  gp : ffffffff81a1ea70 tp : ffffffff8180f500 t0 : ffffffe07fe30000
> [    0.000000]  t1 : 0000000000000004 t2 : 0000000000000000 s0 : ffffffff81803e60
> [    0.000000]  s1 : 0000000000000000 a0 : ffffffff81a22238 a1 : ffffffff81803e10
> [    0.000000]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
> [    0.000000]  a5 : 0000000000000000 a6 : ffffffff8000989c a7 : 0000000052464e43
> [    0.000000]  s2 : ffffffff81a220c8 s3 : 0000000000000000 s4 : 0000000000000000
> [    0.000000]  s5 : 0000000000000000 s6 : 0000000200000100 s7 : 0000000000000001
> [    0.000000]  s8 : ffffffe07fe04040 s9 : ffffffff81a22c80 s10: 0000000000001000
> [    0.000000]  s11: 0000000000000004 t3 : 0000000000000001 t4 : 0000000000000008
> [    0.000000]  t5 : ffffffcf04000808 t6 : ffffffe3ffddf188
> [    0.000000] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000002
> [    0.000000] [<ffffffff80007240>] riscv_cpuid_to_hartid_mask+0x6/0xae
> [    0.000000] [<ffffffff80009474>] sbi_remote_fence_i+0x1e/0x26
> [    0.000000] [<ffffffff8000b8f4>] flush_icache_all+0x12/0x1a
> [    0.000000] [<ffffffff8000666c>] patch_text_nosync+0x26/0x32
> [    0.000000] [<ffffffff8000884e>] ftrace_init_nop+0x52/0x8c
> [    0.000000] [<ffffffff800f051e>] ftrace_process_locs.isra.0+0x29c/0x360
> [    0.000000] [<ffffffff80a0e3c6>] ftrace_init+0x80/0x130
> [    0.000000] [<ffffffff80a00f8c>] start_kernel+0x5c4/0x8f6
> [    0.000000] ---[ end trace f67eb9af4d8d492b ]---
> [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
>
> While ftrace is looping over a list of addresses to patch, it always failed
> when patching the same function: riscv_cpuid_to_hartid_mask. Looking at the
> backtrace, the illegal instruction is encountered in this same function.
> However, patch_text_nosync, after patching the instructions, calls
> flush_icache_range. But looking at what happens in this function:
>
> flush_icache_range -> flush_icache_all
>                    -> sbi_remote_fence_i
>                    -> __sbi_rfence_v02
>                    -> riscv_cpuid_to_hartid_mask
>
> The icache and dcache of the current cpu are never synchronized between the
> patching of riscv_cpuid_to_hartid_mask and calling this same function.
>
> So fix this by flushing the current cpu's icache before asking for the other
> cpus to do the same.
>
> Signed-off-by: Alexandre Ghiti <alex at ghiti.fr>
> ---
>  arch/riscv/mm/cacheflush.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 094118663285..89f81067e09e 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -16,6 +16,8 @@ static void ipi_remote_fence_i(void *info)
>
>  void flush_icache_all(void)
>  {
> +	local_flush_icache_all();
> +
>  	if (IS_ENABLED(CONFIG_RISCV_SBI))
>  		sbi_remote_fence_i(NULL);
>  	else

Thanks, this is on fixes (with the tags for stable)