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

["Roger Pau Monné" <roger.pau@citrix.com>]

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?

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.

Thanks, Roger.

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