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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Yes.

> 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.

Jan


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