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: <Y2A6/ZwvKhpNBTMP@zn.tnic>
Date:   Mon, 31 Oct 2022 22:15:41 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kalra, Ashish" <ashish.kalra@....com>
Cc:     vbabka@...e.cz, 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,
        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, Oct 31, 2022 at 03:10:16PM -0500, Kalra, Ashish wrote:
> Just to add here, writing to any of these pages from the Host
> will trigger a RMP #PF which will cause the RMP page fault handler
> to send a SIGBUS to the current process, as this page is not owned
> by Host.

And kill the host process?

So this is another "policy" which sounds iffy. If we kill the process,
we should at least say why. Are we doing that currently?

> So calling memory_failure() is proactively doing the same, marking the
> page as poisoned and probably also killing the current process.

But the page is not suffering a memory failure - it cannot be reclaimed
for whatever reason. Btw, how can that reclaim failure ever happen? Any
real scenarios?

Anyway, memory failure just happens to fit what you wanna do but you
can't just reuse that - that's hacky. What is the problem with writing
your own function which does that?

Also, btw, please do not top-post.

Thx.

-- 
Regards/Gruss,
    Boris.

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