[PATCHV4 2/3] x86, ras: Extend machine check recovery code to annotated ring0 areas

Tony Luck
2015-12-24T21:10:09Z

Extend the severity checking code to add a new context IN_KERN_RECOV
which is used to indicate that the machine check was triggered by code
in the kernel with a fixup entry.

Add code to check for this situation and respond by altering the return
IP to the fixup address.

Major re-work to the tail code in do_machine_check() to make all this
readable/maintainable. One functional change is that tolerant=3 no longer
stops recovery actions. Revert to only skipping sending SIGBUS to the
current process.

Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/kernel/cpu/mcheck/mce-severity.c | 21 +++++++++-
arch/x86/kernel/cpu/mcheck/mce.c | 70 ++++++++++++++++---------------
2 files changed, 55 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce-severity.c b/arch/x86/kernel/cpu/mcheck/mce-severity.c
index 9c682c222071..cc7136351820 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -29,7 +29,7 @@
* panic situations)
*/

-enum context { IN_KERNEL = 1, IN_USER = 2 };
+enum context { IN_KERNEL = 1, IN_USER = 2, IN_KERNEL_RECOV = 3 };
enum ser { SER_REQUIRED = 1, NO_SER = 2 };
enum exception { EXCP_CONTEXT = 1, NO_EXCP = 2 };

@@ -48,6 +48,7 @@ static struct severity {
#define MCESEV(s, m, c...) { .sev = MCE_ ## s ## _SEVERITY, .msg = m, ## c }
#define KERNEL .context = IN_KERNEL
#define USER .context = IN_USER
+#define KERNEL_RECOV .context = IN_KERNEL_RECOV
#define SER .ser = SER_REQUIRED
#define NOSER .ser = NO_SER
#define EXCP .excp = EXCP_CONTEXT
@@ -87,6 +88,10 @@ static struct severity {
EXCP, KERNEL, MCGMASK(MCG_STATUS_RIPV, 0)
),
MCESEV(
+ PANIC, "In kernel and no restart IP",
+ EXCP, KERNEL_RECOV, MCGMASK(MCG_STATUS_RIPV, 0)
+ ),
+ MCESEV(
DEFERRED, "Deferred error",
NOSER, MASK(MCI_STATUS_UC|MCI_STATUS_DEFERRED|MCI_STATUS_POISON, MCI_STATUS_DEFERRED)
),
@@ -123,6 +128,11 @@ static struct severity {
MCGMASK(MCG_STATUS_RIPV|MCG_STATUS_EIPV, MCG_STATUS_RIPV)
),
MCESEV(
+ AR, "Action required: data load in error recoverable area of kernel",
+ SER, MASK(MCI_STATUS_OVER|MCI_UC_SAR|MCI_ADDR|MCACOD, MCI_UC_SAR|MCI_ADDR|MCACOD_DATA),
+ KERNEL_RECOV
+ ),
+ MCESEV(
AR, "Action required: data load error in a user process",
SER, MASK(MCI_STATUS_OVER|MCI_UC_SAR|MCI_ADDR|MCACOD, MCI_UC_SAR|MCI_ADDR|MCACOD_DATA),
USER
@@ -170,6 +180,9 @@ static struct severity {
) /* always matches. keep at end */
};

+#define mc_recoverable(mcg) (((mcg) & (MCG_STATUS_RIPV|MCG_STATUS_EIPV)) == \
+ (MCG_STATUS_RIPV|MCG_STATUS_EIPV))
+
/*
* If mcgstatus indicated that ip/cs on the stack were
* no good, then "m->cs" will be zero and we will have
@@ -183,7 +196,11 @@ static struct severity {
*/
static int error_context(struct mce *m)
{
- return ((m->cs & 3) == 3) ? IN_USER : IN_KERNEL;
+ if ((m->cs & 3) == 3)
+ return IN_USER;
+ if (mc_recoverable(m->mcgstatus) && search_mcexception_tables(m->ip))
+ return IN_KERNEL_RECOV;
+ return IN_KERNEL;
}

/*
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 0111cd49ee94..e848b583e840 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -959,6 +959,20 @@ static void mce_clear_state(unsigned long *toclear)
}
}

+static int do_memory_failure(struct mce *m)
+{
+ int flags = MF_ACTION_REQUIRED;
+ int ret;
+
+ pr_err("Uncorrected hardware memory error in user-access at %llx", m->addr);
+ if (!(m->mcgstatus & MCG_STATUS_RIPV))
+ flags |= MF_MUST_KILL;
+ ret = memory_failure(m->addr >> PAGE_SHIFT, MCE_VECTOR, flags);
+ if (ret)
+ pr_err("Memory error not recovered");
+ return ret;
+}
+
/*
* The actual machine check handler. This only handles real
* exceptions when something got corrupted coming in through int 18.
@@ -996,8 +1010,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
DECLARE_BITMAP(toclear, MAX_NR_BANKS);
DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
char *msg = "Unknown";
- u64 recover_paddr = ~0ull;
- int flags = MF_ACTION_REQUIRED;
int lmce = 0;

ist_enter(regs);
@@ -1124,22 +1136,13 @@ void do_machine_check(struct pt_regs *regs, long error_code)
}

/*
- * At insane "tolerant" levels we take no action. Otherwise
- * we only die if we have no other choice. For less serious
- * issues we try to recover, or limit damage to the current
- * process.
+ * If tolerant is at an insane level we drop requests to kill
+ * processes and continue even when there is no way out.
*/
- if (cfg->tolerant < 3) {
- if (no_way_out)
- mce_panic("Fatal machine check on current CPU", &m, msg);
- if (worst == MCE_AR_SEVERITY) {
- recover_paddr = m.addr;
- if (!(m.mcgstatus & MCG_STATUS_RIPV))
- flags |= MF_MUST_KILL;
- } else if (kill_it) {
- force_sig(SIGBUS, current);
- }
- }
+ if (cfg->tolerant == 3)
+ kill_it = 0;
+ else if (no_way_out)
+ mce_panic("Fatal machine check on current CPU", &m, msg);

if (worst > 0)
mce_report_event(regs);
@@ -1147,25 +1150,24 @@ void do_machine_check(struct pt_regs *regs, long error_code)
out:
sync_core();

- if (recover_paddr == ~0ull)
- goto done;
+ if (worst != MCE_AR_SEVERITY && !kill_it)
+ goto out_ist;

- pr_err("Uncorrected hardware memory error in user-access at %llx",
- recover_paddr);
- /*
- * We must call memory_failure() here even if the current process is
- * doomed. We still need to mark the page as poisoned and alert any
- * other users of the page.
- */
- ist_begin_non_atomic(regs);
- local_irq_enable();
- if (memory_failure(recover_paddr >> PAGE_SHIFT, MCE_VECTOR, flags) < 0) {
- pr_err("Memory error not recovered");
- force_sig(SIGBUS, current);
+ /* Fault was in user mode and we need to take some action */
+ if ((m.cs & 3) == 3) {
+ ist_begin_non_atomic(regs);
+ local_irq_enable();
+
+ if (kill_it || do_memory_failure(&m))
+ force_sig(SIGBUS, current);
+ local_irq_disable();
+ ist_end_non_atomic();
+ } else {
+ if (!fixup_mcexception(regs))
+ mce_panic("Failed kernel mode recovery", &m, NULL);
}
- local_irq_disable();
- ist_end_non_atomic();
-done:
+
+out_ist:
ist_exit(regs);
}
EXPORT_SYMBOL_GPL(do_machine_check);
--
2.1.4