linux-kernel - Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled

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Message-ID: <Y3yhthJTIWqjjAPK@zn.tnic>
Date:   Tue, 22 Nov 2022 11:17:26 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kalra, Ashish" <ashish.kalra@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        michael.roth@....com, vbabka@...e.cz, kirill@...temov.name,
        ak@...ux.intel.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled

On Mon, Nov 21, 2022 at 06:37:18PM -0600, Kalra, Ashish wrote:
> I agree, but these pages are not in the right state to be released back to

Which pages exactly?

Some pages' state has really changed underneath or you've given the
wrong range?

> It might be a user/sev-guest error, but these pages are now unsafe to use.
> So is a kernel panic justified here, instead of not releasing the pages back
> to host and logging errors for the same.

Ok, there are two cases:

* kernel error: I guess a big fat warning is the least we can issue
here. Not sure about panic considering this should almost never happen
and a warning would allow for people to catch dumps and debug the issue.

* firmware error: I don't think you can know that that is really
the case on a production system without additional fw debugging
capabilities. Dumping a warning would be the least we can do here too,
to signal that something's out of the ordinary and so people can look
into it further.

So yeah, a big fat warning is a good start. And then you don't need any
memory poisoning etc gunk.

-- 
Regards/Gruss,
    Boris.

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