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

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Date:   Tue, 25 Oct 2022 12:25:36 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Kalra, Ashish" <ashish.kalra@....com>, vbabka@...e.cz
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, 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 Fri, Oct 14, 2022 at 03:00:09PM -0500, Kalra, Ashish wrote:
> If it is "still" accessed/touched then it can cause RMP #PF.
> On the other hand,
> 
>  * PG_hwpoison... Accessing is
>  * not safe since it may cause another machine check. Don't touch!
> 
> That sounds exactly the state we want these page(s) to be in ?
> 
> Another possibility is PG_error.

Something like this:

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e66f7aa3191d..baffa9c0dc30 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -186,6 +186,7 @@ enum pageflags {
 	 * THP.
 	 */
 	PG_has_hwpoisoned = PG_error,
+	PG_offlimits = PG_hwpoison,
 #endif
 
 	/* non-lru isolated movable page */

and SNP will have to depend on CONFIG_MEMORY_FAILURE.

But I'd let mm folks correct me here on the details.

-- 
Regards/Gruss,
    Boris.

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