Re: [PATCH 1/5] x86/mce/inject: Check if a bank is unpopulated before error simulation

[Smita Koralahalli Channabasappa]

Hi Boris,

On 9/24/21 3:26 AM, Borislav Petkov wrote:

> On Wed, Sep 15, 2021 at 06:27:35PM -0500, Smita Koralahalli wrote:
> > The MCA_IPID register uniquely identifies a bank's type on Scalable MCA
> > (SMCA) systems. When an MCA bank is not populated, the MCA_IPID register
> > will read as zero and writes to it will be ignored. Check the value of
> > this register before trying to simulate the error.
> >
> > Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
> > ---
> >   arch/x86/kernel/cpu/mce/inject.c | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
> > index 0bfc14041bbb..51ac575c4605 100644
> > --- a/arch/x86/kernel/cpu/mce/inject.c
> > +++ b/arch/x86/kernel/cpu/mce/inject.c
> > @@ -577,6 +577,24 @@ static int inj_bank_set(void *data, u64 val)
> >   	}
> >
> > +	if (boot_cpu_has(X86_FEATURE_SMCA)) {
> This whole thing belongs into inj_ipid_set() where you should verify
> whether the bank is set when you try to set the IPID for that bank.

Can you please elaborate on this? I'm not sure if I understood this
right. Should I read the ipid file to verify that the user has input
proper ipid? If ipid file reads zero then do rdmsrl_on_cpu?

Thanks,
Smita

> +			if (!m->ipid) {
> +				pr_err("Error simulation not possible: Bank %llu unpopulated\n",
> > +
> > +		/* Check for user provided IPID value. */
> > +		if (!m->ipid) {
> > +			rdmsrl_on_cpu(m->extcpu, MSR_AMD64_SMCA_MCx_IPID(val),
> > +				      &m->ipid);
> Oh well, one IPI per ipid write. We're doing injection so we can't be on
> a production machine so who cares about IPIs there.