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Subject[ 82/94] x86/mce: Fix check for processor context when machine check was taken.
3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tony Luck <tony.luck@intel.com>

commit 875e26648cf9b6db9d8dc07b7959d7c61fb3f49c upstream.

Linus pointed out that there was no value is checking whether m->ip
was zero - because zero is a legimate value. If we have a reliable
(or faked in the VM86 case) "m->cs" we can use it to tell whether we
were in user mode or kernelwhen the machine check hit.

Reported-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/cpu/mcheck/mce-severity.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -145,15 +145,19 @@ static struct severity {
};

/*
- * If the EIPV bit is set, it means the saved IP is the
- * instruction which caused the MCE.
+ * If mcgstatus indicated that ip/cs on the stack were
+ * no good, then "m->cs" will be zero and we will have
+ * to assume the worst case (IN_KERNEL) as we actually
+ * have no idea what we were executing when the machine
+ * check hit.
+ * If we do have a good "m->cs" (or a faked one in the
+ * case we were executing in VM86 mode) we can use it to
+ * distinguish an exception taken in user from from one
+ * taken in the kernel.
*/
static int error_context(struct mce *m)
{
- if (m->mcgstatus & MCG_STATUS_EIPV)
- return (m->ip && (m->cs & 3) == 3) ? IN_USER : IN_KERNEL;
- /* Unknown, assume kernel */
- return IN_KERNEL;
+ return ((m->cs & 3) == 3) ? IN_USER : IN_KERNEL;
}

int mce_severity(struct mce *m, int tolerant, char **msg)



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