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x86/mce: Remove noinstr annotation from mce_setup() 

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@suse.de>
Link: https://lore.kernel.org/r/20211208111343.8130-5-bp@alien8.de
This commit is contained in:
Borislav Petkov 2021-10-05 19:54:47 +02:00
parent 88f66a4235
commit 487d654db3
1 changed files with 20 additions and 6 deletions
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26
arch/x86/kernel/cpu/mce/core.c
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@ -127,7 +127,7 @@ static struct irq_work mce_irq_work;
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();
@ -430,9 +430,15 @@ static noinstr void mce_wrmsrl(u32 msr, u64 v)
* 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) {
@ -1312,11 +1318,11 @@ static noinstr void unexpected_machine_check(struct pt_regs *regs)
}
/*
* 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
@ -1328,6 +1334,14 @@ static noinstr void unexpected_machine_check(struct pt_regs *regs)
* 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)
{