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

[Chao Gao <chao.gao@intel.com>]

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.

Thanks
Chao

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