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Re: [Xen-devel] [PATCH] x86, amd_ucode: Safeguard against #GP

On 5/23/2014 1:05 AM, Jan Beulich wrote:
On 22.05.14 at 17:59, <aravind.gopalakrishnan@xxxxxxx> wrote:
On 5/22/2014 3:44 AM, Jan Beulich wrote:
On 21.05.14 at 23:28, <aravind.gopalakrishnan@xxxxxxx> wrote:
When HW tries to load a corrupted patch, it generates #GP
and hangs the system. Use wrmsr_safe instead so that we
fail to load microcode gracefully.

Example on a Fam15h system-
(XEN) microcode: CPU0 collect_cpu_info: patch_id=0x6000626
(XEN) microcode: CPU0 size 7870, block size 2586 offset 76 equivID
0x6012 rev 0x6000637
(XEN) microcode: CPU0 found a matching microcode update with version
0x6000637 (current=0x6000626)
(XEN) traps.c:3073: GPF (0000): ffff82d08016f682 -> ffff82d08022d9f8
(XEN) microcode: CPU0 update from revision 0x6000637 to 0x6000626 failed

Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>
   xen/arch/x86/microcode_amd.c |    2 +-
   1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index e83f4b6..23637e2 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -191,7 +191,7 @@ static int apply_microcode(int cpu)
spin_lock_irqsave(&microcode_update_lock, flags); - wrmsrl(MSR_AMD_PATCHLOADER, (unsigned long)hdr);
+    wrmsr_safe(MSR_AMD_PATCHLOADER, (unsigned long)hdr);
I think you shouldn't ignore the "return" value here.
Not sure I understand..
Do you mean you want to capture return value and bubble it up? maybe
print a debug message too?

Since we check if patch application succeeded using -
if ( rev != hdr->patch_id )
and return a error val here, would this not be sufficient?
It might, but I'm of the opinion that errors should never be ignored
_and_ be detected as early as possible.

Have addressed above issues and sending out V2 with Boris' Reviewed-by tag.


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