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Subject[PATCH 1/2] x86/mce: Only restart instruction after machine check recovery if it is safe
Section 15.3.1.2 of the software developer manual has this to say about the
RIPV bit in the IA32_MCG_STATUS register:

RIPV (restart IP valid) flag, bit 0 — Indicates (when set) that program
execution can be restarted reliably at the instruction pointed to by the
instruction pointer pushed on the stack when the machine-check exception
is generated. When clear, the program cannot be reliably restarted at
the pushed instruction pointer.

We need to save the state of this bit in do_machine_check() and use it
in mce_notify_process() to force a signal; even if memory_failure() says
it made a complete recovery ... e.g. replaced a clean LRU page).

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/kernel/cpu/mcheck/mce.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 66e1c51..3b8ebdc 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -947,9 +947,10 @@ struct mce_info {
atomic_t inuse;
struct task_struct *t;
__u64 paddr;
+ int restartable;
} mce_info[MCE_INFO_MAX];

-static void mce_save_info(__u64 addr)
+static void mce_save_info(__u64 addr, int c)
{
struct mce_info *mi;

@@ -957,6 +958,7 @@ static void mce_save_info(__u64 addr)
if (atomic_cmpxchg(&mi->inuse, 0, 1) == 0) {
mi->t = current;
mi->paddr = addr;
+ mi->restartable = c;
return;
}
}
@@ -1136,7 +1138,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
mce_panic("Fatal machine check on current CPU", &m, msg);
if (worst == MCE_AR_SEVERITY) {
/* schedule action before return to userland */
- mce_save_info(m.addr);
+ mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
set_thread_flag(TIF_MCE_NOTIFY);
} else if (kill_it) {
force_sig(SIGBUS, current);
@@ -1185,7 +1187,8 @@ void mce_notify_process(void)

pr_err("Uncorrected hardware memory error in user-access at %llx",
mi->paddr);
- if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0) {
+ if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0 ||
+ mi->restartable == 0) {
pr_err("Memory error not recovered");
force_sig(SIGBUS, current);
}
--
1.7.9.rc2.1.g69204
--
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