Re: [PATCH] Fix the message in facility unavailable exception
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2016-11-07 07:53:44
Balbir Singh [off-list ref] writes:
I ran into this during some testing on qemu. The current facility_strings[] are correct when the trap address is 0xf80 (hypervisor facility unavailable). When the trap address is 0xf60, IC (Interruption Cause) a.k.a status in the code is undefined for values 0 and 1.
OK. But how did you generate an exception with an undefined status code?
quoted hunk ↗ jump to hunk
This patch adds a check to prevent printing the wrong information and helps better direct debugging effort.diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index d26605d..da0f634 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c@@ -1520,8 +1520,14 @@ void facility_unavailable_exception(struct pt_regs *regs) } if ((status < ARRAY_SIZE(facility_strings)) && - facility_strings[status]) - facility = facility_strings[status]; + facility_strings[status]) { + if (!hv && status < 2) { + pr_warn("Unexpected facility unavailable exception " + "interruption cause %d\n", status);
Please don't add un-ratelimited printks() in this function, otherwise if they're user triggerable (which some are) it gives the user a way to scrub the kernel log.
+ facility = "Unknown"; + } else + facility = facility_strings[status]; + }
I think we should instead tighten the condition on that top-level if, and
have an else clause for all cases that uses "Unknown". eg.
if ((hv || status >= 2) &&
(status < ARRAY_SIZE(facility_strings)) &&
facility_strings[status])
{
facility = facility_strings[status];
} else {
facility = "Unknown";
}
And then if you want to we can also print the hex status value in the
existing printk().
cheers