6.17-stable review patch. If anyone has any objections, please let me know.
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From: Rong Zhang i@rong.moe
commit e6416c2dfe23c9a6fec881fda22ebb9ae486cfc5 upstream.
The S5_RESET_STATUS register is parsed on boot and printed to kmsg. However, this could sometimes be misleading and lead to users wasting a lot of time on meaningless debugging for two reasons:
* Some bits are never cleared by hardware. It's the software's responsibility to clear them as per the Processor Programming Reference (see [1]).
* Some rare hardware-initiated platform resets do not update the register at all.
In both cases, a previous reboot could leave its trace in the register, resulting in users seeing unrelated reboot reasons while debugging random reboots afterward.
Write the read value back to the register in order to clear all reason bits since they are write-1-to-clear while the others must be preserved.
[1]: https://bugzilla.kernel.org/show_bug.cgi?id=206537#attach_303991
[ bp: Massage commit message. ]
Fixes: ab8131028710 ("x86/CPU/AMD: Print the reason for the last reset") Signed-off-by: Rong Zhang i@rong.moe Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Mario Limonciello (AMD) superm1@kernel.org Reviewed-by: Yazen Ghannam yazen.ghannam@amd.com Cc: stable@kernel.org Link: https://lore.kernel.org/all/20250913144245.23237-1-i@rong.moe/ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/amd.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1338,11 +1338,23 @@ static __init int print_s5_reset_status_ return 0;
value = ioread32(addr); - iounmap(addr);
/* Value with "all bits set" is an error response and should be ignored. */ - if (value == U32_MAX) + if (value == U32_MAX) { + iounmap(addr); return 0; + } + + /* + * Clear all reason bits so they won't be retained if the next reset + * does not update the register. Besides, some bits are never cleared by + * hardware so it's software's responsibility to clear them. + * + * Writing the value back effectively clears all reason bits as they are + * write-1-to-clear. + */ + iowrite32(value, addr); + iounmap(addr);
for (i = 0; i < ARRAY_SIZE(s5_reset_reason_txt); i++) { if (!(value & BIT(i)))