This is a note to let you know that I've just added the patch titled
x86/mce: Remove noinstr annotation from mce_setup()
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mce-remove-noinstr-annotation-from-mce_setup.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 487d654db3edacc31dee86b10258cc740640fad8 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@xxxxxxx>
Date: Tue, 5 Oct 2021 19:54:47 +0200
Subject: x86/mce: Remove noinstr annotation from mce_setup()
From: Borislav Petkov <bp@xxxxxxx>
commit 487d654db3edacc31dee86b10258cc740640fad8 upstream.
Instead, sandwitch around the call which is done in noinstr context and
mark the caller - mce_gather_info() - as noinstr.
Also, document what the whole instrumentation strategy with #MC is going
to be in the future and where it all is supposed to be going to.
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lore.kernel.org/r/20211208111343.8130-5-bp@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/mce/core.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -130,7 +130,7 @@ static void (*quirk_no_way_out)(int bank
BLOCKING_NOTIFIER_HEAD(x86_mce_decoder_chain);
/* Do initial initialization of a struct mce */
-noinstr void mce_setup(struct mce *m)
+void mce_setup(struct mce *m)
{
memset(m, 0, sizeof(struct mce));
m->cpu = m->extcpu = smp_processor_id();
@@ -479,9 +479,15 @@ static noinstr void mce_wrmsrl(u32 msr,
* check into our "mce" struct so that we can use it later to assess
* the severity of the problem as we read per-bank specific details.
*/
-static inline void mce_gather_info(struct mce *m, struct pt_regs *regs)
+static noinstr void mce_gather_info(struct mce *m, struct pt_regs *regs)
{
+ /*
+ * Enable instrumentation around mce_setup() which calls external
+ * facilities.
+ */
+ instrumentation_begin();
mce_setup(m);
+ instrumentation_end();
m->mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
if (regs) {
@@ -1327,11 +1333,11 @@ static void queue_task_work(struct mce *
}
/*
- * The actual machine check handler. This only handles real
- * exceptions when something got corrupted coming in through int 18.
+ * The actual machine check handler. This only handles real exceptions when
+ * something got corrupted coming in through int 18.
*
- * This is executed in NMI context not subject to normal locking rules. This
- * implies that most kernel services cannot be safely used. Don't even
+ * This is executed in #MC context not subject to normal locking rules.
+ * This implies that most kernel services cannot be safely used. Don't even
* think about putting a printk in there!
*
* On Intel systems this is entered on all CPUs in parallel through
@@ -1343,6 +1349,14 @@ static void queue_task_work(struct mce *
* issues: if the machine check was due to a failure of the memory
* backing the user stack, tracing that reads the user stack will cause
* potentially infinite recursion.
+ *
+ * Currently, the #MC handler calls out to a number of external facilities
+ * and, therefore, allows instrumentation around them. The optimal thing to
+ * have would be to do the absolutely minimal work required in #MC context
+ * and have instrumentation disabled only around that. Further processing can
+ * then happen in process context where instrumentation is allowed. Achieving
+ * that requires careful auditing and modifications. Until then, the code
+ * allows instrumentation temporarily, where required. *
*/
noinstr void do_machine_check(struct pt_regs *regs)
{
Patches currently in stable-queue which might be from bp@xxxxxxx are
queue-5.15/x86-mce-remove-noinstr-annotation-from-mce_setup.patch
