Re: [PATCH v3 3/3] x86/mce: Add CMCI storm switching support for Zhaoxin

[Yazen Ghannam <yazen.ghannam@amd.com>]

On Fri, Sep 20, 2024 at 11:44:59AM +0000, Zhuo, Qiuxu wrote:
> > From: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
> > [...]
> > >> --- a/arch/x86/kernel/cpu/mce/zhaoxin.c
> > >> +++ b/arch/x86/kernel/cpu/mce/zhaoxin.c
> > >> @@ -63,3 +63,21 @@ void mce_zhaoxin_feature_clear(struct cpuinfo_x86
> > >> *c) {
> > >>        intel_clear_lmce();
> > >>   }
> > >> +
> > >> +void mce_zhaoxin_handle_storm(int bank, bool on) {
> > >> +     unsigned long flags;
> > >> +     u64 val;
> > >> +
> > >> +     raw_spin_lock_irqsave(&cmci_discover_lock, flags);
> > >> +     rdmsrl(MSR_IA32_MCx_CTL2(bank), val);
> > >> +     if (on) {
> > >> +             val &= ~(MCI_CTL2_CMCI_EN |
> > >> MCI_CTL2_CMCI_THRESHOLD_MASK);
> > >> +             val |= CMCI_STORM_THRESHOLD;
> > >> +     } else {
> > >> +             val &= ~MCI_CTL2_CMCI_THRESHOLD_MASK;
> > >> +             val |= (MCI_CTL2_CMCI_EN | cmci_threshold[bank]);
> > >> +     }
> > >> +     wrmsrl(MSR_IA32_MCx_CTL2(bank), val);
> > >> +     raw_spin_unlock_irqrestore(&cmci_discover_lock, flags); }
> > >
> > > Are there any reasons or comments why it needs to disable/enable the
> > > CMCI interrupt here during a CMCI storm on/off? If not, then reuse
> > > mce_intel_handle_storm() to avoid duplicating the code.
> > >
> > 
> > As explained in another email.
> > The reason is actually mentioned in the cover letter: "because Zhaoxin's UCR
> > error is not reported through CMCI", and we want to disable CMCI interrupt
> > when CMCI storm happened.
> 
> So, this is just you want to disable CMCI when a CMCI storm happens. 
> This doesn't explain much to me.
> What's the problem if not disable CMCI when a CMCI storm happens?
>

A more direct way to handle an interrupt storm is to turn off the
interrupt. The proposed AMD solution would also do this.

Reprogramming the threshold to a high value does not 100% guarantee that
a storm will be mitigated. But this is a necessary trade-off given that
the CMCI is used to report other error types on Intel systems.

Thanks,
Yazen