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 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?

It would be nice to have paired calls to start_update/end_update in
the same context (ie: function) or else this is very hard to follow,
and very easy to get out of sync.

Thanks, Roger.

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