[tip: x86/urgent] x86/mce: Do not overwrite no_way_out if mce_end() fails

[tip-bot2 for Gabriele Paoloni]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     25bc65d8ddfc17cc1d7a45bd48e9bdc0e729ced3
Gitweb:        https://git.kernel.org/tip/25bc65d8ddfc17cc1d7a45bd48e9bdc0e729ced3
Author:        Gabriele Paoloni <gabriele.paoloni@xxxxxxxxx>
AuthorDate:    Fri, 27 Nov 2020 16:18:15 
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 27 Nov 2020 17:38:36 +01:00

x86/mce: Do not overwrite no_way_out if mce_end() fails

Currently, if mce_end() fails, no_way_out - the variable denoting
whether the machine can recover from this MCE - is determined by whether
the worst severity that was found across the MCA banks associated with
the current CPU, is of panic severity.

However, at this point no_way_out could have been already set by
mca_start() after looking at all severities of all CPUs that entered the
MCE handler. If mce_end() fails, check first if no_way_out is already
set and, if so, stick to it, otherwise use the local worst value.

 [ bp: Massage. ]

Signed-off-by: Gabriele Paoloni <gabriele.paoloni@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201127161819.3106432-2-gabriele.paoloni@xxxxxxxxx
---
 arch/x86/kernel/cpu/mce/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 4102b86..32b7099 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1384,8 +1384,10 @@ noinstr void do_machine_check(struct pt_regs *regs)
 	 * When there's any problem use only local no_way_out state.
 	 */
 	if (!lmce) {
-		if (mce_end(order) < 0)
-			no_way_out = worst >= MCE_PANIC_SEVERITY;
+		if (mce_end(order) < 0) {
+			if (!no_way_out)
+				no_way_out = worst >= MCE_PANIC_SEVERITY;
+		}
 	} else {
 		/*
 		 * If there was a fatal machine check we should have