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

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Message-ID: <YU2Lm+11Pqg/RBK3@zn.tnic>
Date:   Fri, 24 Sep 2021 10:26:03 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Cc:     x86@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>, yazen.ghannam@....com
Subject: Re: [PATCH 1/5] x86/mce/inject: Check if a bank is unpopulated
 before error simulation

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@....com>
> ---
>  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)
>  	}
>  
>  	m->bank = val;
> +
> +	/* Read IPID value to determine if a bank is unpopulated on the target
> +	 * CPU.
> +	 */

Kernel comments style format is:

	/*
	 * A sentence ending with a full-stop.
	 * Another sentence. ...
	 * More sentences. ...
	 */

> +	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.

> +
> +		/* 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.

> +			if (!m->ipid) {
> +				pr_err("Error simulation not possible: Bank %llu unpopulated\n",


"Cannot set IPID for bank... - bank %d unpopulated\n"

Also, in all your text, use "injection" instead of "simulation" so that
there's no confusion.

Thx.

-- 
Regards/Gruss,
    Boris.

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