Re: [Xen-devel] [PATCH 2/2] microcode: Check whether the microcode is correct.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/09/13 14:59, Konrad Rzeszutek Wilk wrote:
> On Wed, Sep 25, 2013 at 02:13:40PM +0100, Andrew Cooper wrote:
>> On 25/09/13 13:57, Konrad Rzeszutek Wilk wrote:
>>> We do the microcode code update in two steps - the presmp:
>>>  'microcode_presmp_init' and when CPUs are brought up:
>>> 'microcode_init'. The earlier performs the microcode update
>>> on the BSP - but unfortunately it does not check whether the
>>> update failed. Which means that we might try later to update
>>> a incorrect payload on the rest of CPUs.
>>>
>>> This patch handles this odd situation.
>>>
>>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> While not strictly relevant to this patch, I simply noticed when
>> reviewing it that ucode_blob is __initdata.  Given the comment "The
>> cached microcode patch is applied when CPUs resume from a sleep state."
>> in the previous patch, what is the policy for reloading microcode after
>> deep sleep / cpu hotplug ?
> The underlaying architecture microcode (microcode_intel or microcode_amd)
> end up saving it in 'struct ucode_cpu_info' which is a per-cpu data
> structure (see ucode_cpu_info). They end up saving it when doing the
> pre-SMP (for CPU0) and SMP (for the rest) microcode loading.
>
> And naturally if one does a hypercall to update the microcode and it is
> newer, then the old per-cpu data is replaced.

Ah ok - I missed that.

>
> Would you like me to update the git commit description with this?

It might be worth having a note to this effect in the commit message of
the previous patch.

~Andrew

>>> [v2: Redid it as we are not doing scan and <index> at the same time]
>>> ---
>>>  xen/arch/x86/microcode.c | 16 +++++++++++++++-
>>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
>>> index 8136d44..0bc95e6 100644
>>> --- a/xen/arch/x86/microcode.c
>>> +++ b/xen/arch/x86/microcode.c
>>> @@ -419,6 +419,7 @@ static int __init microcode_presmp_init(void)
>>>          {
>>>              void *data;
>>>              size_t len;
>>> +            int rc = 0;
>>>  
>>>              if ( ucode_blob.size )
>>>              {
>>> @@ -431,10 +432,23 @@ static int __init microcode_presmp_init(void)
>>>                  data = ucode_mod_map(&ucode_mod);
>>>              }
>>>              if ( data )
>>> -                microcode_update_cpu(data, len);
>>> +                rc = microcode_update_cpu(data, len);
>>> +            else
>>> +                rc = -ENOMEM;
>>>  
>>>              if ( !ucode_blob.size )
>>>                  ucode_mod_map(NULL);
>>> +
>>> +            if ( rc )
>>> +            {
>>> +                if ( ucode_blob.size )
>>> +                {
>>> +                    xfree(ucode_blob.data);
>>> +                    ucode_blob.size = 0;
>>> +                    ucode_blob.data = NULL;
>>> +                } else
>>> +                    ucode_mod.mod_end = 0;
>>> +            }
>>>          }
>>>  
>>>          register_cpu_notifier(&microcode_percpu_nfb);


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