Re: [Xen-devel] [PATCH v9 11/15] microcode: unify loading update during CPU resuming and AP wakeup

[Jan Beulich <jbeulich@suse.com>]

On 29.08.2019 09:37, Chao Gao wrote:
> On Fri, Aug 23, 2019 at 11:09:07AM +0200, Roger Pau Monné wrote:
>> On Fri, Aug 23, 2019 at 12:44:34AM +0800, Chao Gao wrote:
>>> On Thu, Aug 22, 2019 at 04:10:46PM +0200, Roger Pau Monné wrote:
>>>> On Mon, Aug 19, 2019 at 09:25:24AM +0800, Chao Gao wrote:
>>>>> Both are loading the cached patch. Since APs call the unified function,
>>>>> microcode_update_one(), during wakeup, the 'start_update' parameter
>>>>> which originally used to distinguish BSP and APs is redundant. So remove
>>>>> this parameter.
>>>>>
>>>>> Signed-off-by: Chao Gao <chao.gao@intel.com>
>>>>> ---
>>>>> Note that here is a functional change: resuming a CPU would call
>>>>> ->end_update() now while previously it wasn't. Not quite sure
>>>>> whether it is correct.
>>>>
>>>> I guess that's required if it called start_update prior to calling
>>>> end_update?
>>>>
>>>>>
>>>>> Changes in v9:
>>>>>  - return -EOPNOTSUPP rather than 0 if microcode_ops is NULL in
>>>>>    microcode_update_one()
>>>>>  - rebase and fix conflicts.
>>>>>
>>>>> Changes in v8:
>>>>>  - split out from the previous patch
>>>>> ---
>>>>>  xen/arch/x86/acpi/power.c       |  2 +-
>>>>>  xen/arch/x86/microcode.c        | 90 ++++++++++++++++++-----------------------
>>>>>  xen/arch/x86/smpboot.c          |  5 +--
>>>>>  xen/include/asm-x86/processor.h |  4 +-
>>>>>  4 files changed, 44 insertions(+), 57 deletions(-)
>>>>>
>>>>> diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
>>>>> index 4f21903..24798d5 100644
>>>>> --- a/xen/arch/x86/acpi/power.c
>>>>> +++ b/xen/arch/x86/acpi/power.c
>>>>> @@ -253,7 +253,7 @@ static int enter_state(u32 state)
>>>>>  
>>>>>      console_end_sync();
>>>>>  
>>>>> -    microcode_resume_cpu();
>>>>> +    microcode_update_one();
>>>>>  
>>>>>      if ( !recheck_cpu_features(0) )
>>>>>          panic("Missing previously available feature(s)\n");
>>>>> diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
>>>>> index a2febc7..bdd9c9f 100644
>>>>> --- a/xen/arch/x86/microcode.c
>>>>> +++ b/xen/arch/x86/microcode.c
>>>>> @@ -203,24 +203,6 @@ static struct microcode_patch *parse_blob(const char *buf, uint32_t len)
>>>>>      return NULL;
>>>>>  }
>>>>>  
>>>>> -int microcode_resume_cpu(void)
>>>>> -{
>>>>> -    int err;
>>>>> -    struct cpu_signature *sig = &this_cpu(cpu_sig);
>>>>> -
>>>>> -    if ( !microcode_ops )
>>>>> -        return 0;
>>>>> -
>>>>> -    spin_lock(&microcode_mutex);
>>>>> -
>>>>> -    err = microcode_ops->collect_cpu_info(sig);
>>>>> -    if ( likely(!err) )
>>>>> -        err = microcode_ops->apply_microcode(microcode_cache);
>>>>> -    spin_unlock(&microcode_mutex);
>>>>> -
>>>>> -    return err;
>>>>> -}
>>>>> -
>>>>>  void microcode_free_patch(struct microcode_patch *microcode_patch)
>>>>>  {
>>>>>      microcode_ops->free_patch(microcode_patch->mc);
>>>>> @@ -384,11 +366,29 @@ static int __init microcode_init(void)
>>>>>  }
>>>>>  __initcall(microcode_init);
>>>>>  
>>>>> -int __init early_microcode_update_cpu(bool start_update)
>>>>> +/* Load a cached update to current cpu */
>>>>> +int microcode_update_one(void)
>>>>> +{
>>>>> +    int rc;
>>>>> +
>>>>> +    if ( !microcode_ops )
>>>>> +        return -EOPNOTSUPP;
>>>>> +
>>>>> +    rc = microcode_update_cpu(NULL);
>>>>> +
>>>>> +    if ( microcode_ops->end_update )
>>>>> +        microcode_ops->end_update();
>>>>
>>>> Don't you need to call start_update before calling
>>>> microcode_update_cpu?
>>>
>>> No. On AMD side, osvw_status records the hardware erratum in the system.
>>> As we don't assume all CPUs have the same erratum, each cpu calls
>>> end_update to update osvw_status after ucode loading.
>>> start_update just resets osvw_status to 0. And it is called once prior
>>> to ucode loading on any CPU so that osvw_status can be recomputed.
>>
>> Oh, I think I understand it. start_update must only be called once
>> _before_ the sequence to update the microcode on all CPUs is
>> performed, while end_update needs to be called on _each_ CPU after the
>> update has been completed in order to account for any erratas.
>>
>> The name for those hooks should be improved, I guess renaming
>> end_update to end_update_each or end_update_percpu would be clearer in
>> order to make it clear that start_update is global, while end_update
>> is percpu. Anyway, I don't want to delay this series for a naming nit.
>>
>> I'm still unsure where start_update is called for the resume from
>> suspension case, I don't seem to see any call to start_update neither
>> in enter_state or microcode_update_one, hence I think this is missing?
> 
> No. Actually, no call of start_update for resume case.
> 
>>
>> I would expect you need to clean osvw_status also on resume from
>> suspension, in case microcode loading fails? Or else you will be
>> carrying a stale osvw_status.
> 
> Then we need to send IPI to all other CPUs to recompute osvw_state. But
> I think it is not necessary. If ucode cache isn't changed during the
> CPU's suspension period, there is not stale osvw bit (assuming OSVW on
> the resuming CPU won't change). If the ucode cache is updated (there
> must be a late ucode loading), osvw_status should have been cleaned
> before late ucode loading.

I'd actually expect firmware to load whatever ucode it has available,
in which case the OSVW state can very well change across resume. I
agree though that after a successful load of the ucode Xen has
cached that state should be the pre-suspend one again. Yet I guess it
would be more consistent if a proper start-update, ucode-load, end-
update cycle was done even in this case.

Jan

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