[PATCH] x86/MCE/AMD: Allow thresholding interface updates after init

[PATCH] x86/MCE/AMD: Allow thresholding interface updates after init

[Yazen Ghannam]

Changes to the AMD Thresholding sysfs code prevents sysfs writes from
updating the underlying registers once CPU init is completed, i.e.
"threshold_banks" is set.

Allow the registers to be updated if the thresholding interface is
already initialized or if in the init path. Use the "set_lvt_off" value
to indicate if running in the init path, since this value is only set
during init.

Fixes: a037f3ca0ea0 ("x86/mce/amd: Make threshold bank setting hotplug robust")
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
---
 arch/x86/kernel/cpu/mce/amd.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 2eadc7c4c902..408c9546ea0b 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -400,8 +400,12 @@ static void threshold_restart_bank(void *_tr)
 	struct thresh_restart *tr = _tr;
 	u32 hi, lo;
 
-	/* sysfs write might race against an offline operation */
-	if (this_cpu_read(threshold_banks))
+	/*
+	 * sysfs write might race against an offline operation.
+	 * Prevent register writes if threshold_banks are not set and this is
+	 * not called from the init path as indicated by "set_lvt_off".
+	 */
+	if (!(this_cpu_read(threshold_banks) || tr->set_lvt_off))
 		return;
 
 	rdmsr(tr->b->address, lo, hi);
-- 
2.25.1

Re: [PATCH] x86/MCE/AMD: Allow thresholding interface updates after init

[Borislav Petkov]

On Tue, Dec 07, 2021 at 07:30:28PM +0000, Yazen Ghannam wrote:
> Changes to the AMD Thresholding sysfs code prevents sysfs writes from
> updating the underlying registers once CPU init is completed, i.e.
> "threshold_banks" is set.
> 
> Allow the registers to be updated if the thresholding interface is
> already initialized or if in the init path. Use the "set_lvt_off" value
> to indicate if running in the init path, since this value is only set
> during init.
> 
> Fixes: a037f3ca0ea0 ("x86/mce/amd: Make threshold bank setting hotplug robust")
> Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>

We want that in stable, right?

> ---
>  arch/x86/kernel/cpu/mce/amd.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
> index 2eadc7c4c902..408c9546ea0b 100644
> --- a/arch/x86/kernel/cpu/mce/amd.c
> +++ b/arch/x86/kernel/cpu/mce/amd.c
> @@ -400,8 +400,12 @@ static void threshold_restart_bank(void *_tr)
>  	struct thresh_restart *tr = _tr;
>  	u32 hi, lo;
>  
> -	/* sysfs write might race against an offline operation */
> -	if (this_cpu_read(threshold_banks))
> +	/*
> +	 * sysfs write might race against an offline operation.
> +	 * Prevent register writes if threshold_banks are not set and this is
> +	 * not called from the init path as indicated by "set_lvt_off".
> +	 */

So if you convert this text into code, it would read like:

	if (!this_cpu_read(threshold_banks) && !tr->set_lvt_off)

which is equivalent to:

> +	if (!(this_cpu_read(threshold_banks) || tr->set_lvt_off))

but easier to follow, methinks.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] x86/MCE/AMD: Allow thresholding interface updates after init

[Yazen Ghannam]

On Wed, Dec 29, 2021 at 06:42:18PM +0100, Borislav Petkov wrote:
> On Tue, Dec 07, 2021 at 07:30:28PM +0000, Yazen Ghannam wrote:
> > Changes to the AMD Thresholding sysfs code prevents sysfs writes from
> > updating the underlying registers once CPU init is completed, i.e.
> > "threshold_banks" is set.
> > 
> > Allow the registers to be updated if the thresholding interface is
> > already initialized or if in the init path. Use the "set_lvt_off" value
> > to indicate if running in the init path, since this value is only set
> > during init.
> > 
> > Fixes: a037f3ca0ea0 ("x86/mce/amd: Make threshold bank setting hotplug robust")
> > Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
> 
> We want that in stable, right?
>

Yes, thanks for catching that.
 
> > ---
> >  arch/x86/kernel/cpu/mce/amd.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
> > index 2eadc7c4c902..408c9546ea0b 100644
> > --- a/arch/x86/kernel/cpu/mce/amd.c
> > +++ b/arch/x86/kernel/cpu/mce/amd.c
> > @@ -400,8 +400,12 @@ static void threshold_restart_bank(void *_tr)
> >  	struct thresh_restart *tr = _tr;
> >  	u32 hi, lo;
> >  
> > -	/* sysfs write might race against an offline operation */
> > -	if (this_cpu_read(threshold_banks))
> > +	/*
> > +	 * sysfs write might race against an offline operation.
> > +	 * Prevent register writes if threshold_banks are not set and this is
> > +	 * not called from the init path as indicated by "set_lvt_off".
> > +	 */
> 
> So if you convert this text into code, it would read like:
> 
> 	if (!this_cpu_read(threshold_banks) && !tr->set_lvt_off)
> 
> which is equivalent to:
> 
> > +	if (!(this_cpu_read(threshold_banks) || tr->set_lvt_off))
> 
> but easier to follow, methinks.
>

Sure, I'll make the change and send another version.

Thanks,
Yazen