Re: [PATCH v4 1/2] x86/mce: Check for writes ignored in MCA_STATUS register

From: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
To: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Yazen Ghannam <yazen.ghannam@amd.com>
Subject: Re: [PATCH v4 1/2] x86/mce: Check for writes ignored in MCA_STATUS register
Date: Thu, 5 May 2022 12:03:36 -0700	[thread overview]
Message-ID: <f6d7de83-2054-89ab-98a8-b6ada3e6e166@amd.com> (raw)
In-Reply-To: <YnGbHcMkLCsauzXF@zn.tnic>

On 5/3/2022 2:14 PM, Borislav Petkov wrote:
> On Mon, May 02, 2022 at 08:28:47PM -0700, Smita Koralahalli wrote:
>> I'm bit more inclined towards your previous approach of
>> hw_injection_possible
>> check in do_inject(). This seems better than doing it in flags_write().
> If you don't do it in flags_write() then the user would do
>
>     echo "hw" > flags
>
> the command will succeed and the user will think that hw injection is
> possible and then wonder why it fails later.
That's right!
>
> I even actually think that in the first run, when hw_injection_possible
> is not determined yet, you should try to poke at MCi_STATUS of some
> non-reserved bank - and we enumerate which those are at boot in
> __mcheck_cpu_check_banks(), so you can pick a random, non-RAZ bank, save
> its MCi_STATUS, try to write it and if it succeeds, restore it.
>
> This way you'll determine whether hw injection is possible, store it
> in the static hw_injection_possible and then query only that variable.
> I.e., you'll have to poke that MCi_STATUS only once on driver init.

Okay I agree too. I will work on this.

Thanks,
Smita
>   And
> this way it'll be the most optimal, methinks.
>
> Thx.
>