[PATCH AUTOSEL 6.6 34/59] ACPI: APEI: GHES: add TAINT_MACHINE_CHECK on GHES panic path

[Sasha Levin <sashal@kernel.org>]

From: Breno Leitao <leitao@debian.org>

[ Upstream commit 4734c8b46b901cff2feda8b82abc710b65dc31c1 ]

When a GHES (Generic Hardware Error Source) triggers a panic, add the
TAINT_MACHINE_CHECK taint flag to the kernel. This explicitly marks the
kernel as tainted due to a machine check event, improving diagnostics
and post-mortem analysis. The taint is set with LOCKDEP_STILL_OK to
indicate lockdep remains valid.

At large scale deployment, this helps to quickly determine panics that
are coming due to hardware failures.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://patch.msgid.link/20250702-add_tain-v1-1-9187b10914b9@debian.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my analysis of this commit, here is my assessment:

**Backport Status: YES**

This commit should be backported to stable kernel trees for the
following reasons:

1. **Fixes a real diagnostic issue**: The commit adds the
   TAINT_MACHINE_CHECK flag when GHES (Generic Hardware Error Source)
   triggers a panic. This is important for post-mortem analysis at
   scale, as explicitly stated in the commit message: "At large scale
   deployment, this helps to quickly determine panics that are coming
   due to hardware failures."

2. **Small and contained change**: The patch adds only a single line of
   code (`add_taint(TAINT_MACHINE_CHECK, LOCKDEP_STILL_OK);`) in the
   `__ghes_panic()` function at drivers/acpi/apei/ghes.c:1091. This
   meets the stable kernel rule of being under 100 lines.

3. **Obviously correct**: The change follows established kernel
   patterns. Looking at the grep results, other machine check handlers
   already use this same pattern:
   - arch/x86/kernel/cpu/mce/core.c:1640
   - arch/powerpc/kernel/mce.c:332
   - arch/x86/kernel/cpu/mce/p5.c:40
   - arch/x86/kernel/cpu/mce/winchip.c:24

4. **No architectural changes**: This is purely a diagnostic improvement
   that adds taint information without changing any functionality or
   behavior of the GHES panic path.

5. **Minimal risk**: The change uses LOCKDEP_STILL_OK flag, indicating
   that lockdep remains valid after the taint, which is the safer option
   compared to LOCKDEP_NOW_UNRELIABLE used in some other machine check
   paths.

6. **Real benefit for users**: For organizations running Linux at scale,
   being able to quickly identify hardware-related panics through the
   taint flag provides significant operational value for triaging
   issues.

The commit meets all the stable kernel criteria: it's small, obviously
correct, fixes a real diagnostic limitation that affects users
(especially at scale), and has been reviewed by Tony Luck who is a
recognized maintainer in the RAS (Reliability, Availability, and
Serviceability) subsystem.

 drivers/acpi/apei/ghes.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 22db720b128b..ec364c254112 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -912,6 +912,8 @@ static void __ghes_panic(struct ghes *ghes,
 
 	__ghes_print_estatus(KERN_EMERG, ghes->generic, estatus);
 
+	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_STILL_OK);
+
 	ghes_clear_estatus(ghes, estatus, buf_paddr, fixmap_idx);
 
 	if (!panic_timeout)
-- 
2.39.5