linux-kernel - Re: [PATCH v2 2/5] x86/mce/inject: Warn the user on a not set valid bit in MCA

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Date:   Tue, 26 Oct 2021 19:15:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Koralahalli Channabasappa, Smita" <skoralah@....com>
Cc:     Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
        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 v2 2/5] x86/mce/inject: Warn the user on a not set valid
 bit in MCA_STATUS

On Tue, Oct 26, 2021 at 11:58:58AM -0500, Koralahalli Channabasappa, Smita wrote:
> Like how it was done here?
> https://lkml.kernel.org/r/20210915232739.6367-3-Smita.KoralahalliChannabasappa@amd.com

Whoops, sorry about that.

So let's analyze this properly - there are two cases:

1. warn if VAL=0: what does that bring us? The person doing the injection
will simply have to set the valid bit and repeat the injection.

I guess "maybe the user wants to inject with Val not set" doesn't make a
whole lot of sense because nothing will happen - error will get ignored.

So we can do all the warning we want - it will be useless and in some
cases the user might not even see it.

So it sounds to me like setting the valid bit directly makes a lot more
sense.

2. Automatically set VAL=1 to correct any VAL=0 injections.

Yes, we force the VAL bit to 1 and that is not what the user injected
but the user injecting with VAL=0 will get ignored, i.e., it will be
pointless.

So we "help" here and set the valid bit.

Anything else I'm missing?

Sorry again for being back'n'forth on this.

-- 
Regards/Gruss,
    Boris.

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