Commit 487d654d authored by Borislav Petkov's avatar Borislav Petkov
Browse files

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: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211208111343.8130-5-bp@alien8.de
parent 88f66a42

arch/x86/kernel/cpu/mce/core.c

+20 −6
Original line number Diff line number Diff line
@@ -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)

{