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

[Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>]

On 5/23/2014 1:05 AM, Jan Beulich wrote:
>>>> On 22.05.14 at 17:59, <aravind.gopalakrishnan@amd.com> wrote:
>> On 5/22/2014 3:44 AM, Jan Beulich wrote:
>>>>>> On 21.05.14 at 23:28, <aravind.gopalakrishnan@amd.com> 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@amd.com>
>>>> ---
>>>>    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.
>
>
Have addressed above issues and sending out V2 with Boris' Reviewed-by tag.

Thanks,
-Aravind.