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

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Date:   Wed, 16 Nov 2022 10:32:05 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Borislav Petkov <bp@...en8.de>
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,
        "Kaplan, David" <David.Kaplan@....com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled

On 11/16/22 02:25, Vlastimil Babka wrote:
>> Referring back to your thoughts about putting these pages on some leaked
>> pages list, do any such leaked pages list exist currently ?
> Not AFAIK, you could just create a list_head somewhere appropriate (some snp
> state structure?) and put the pages there, maybe with a counter exposed in
> debugs. The point would be mostly that if something goes so wrong it would
> be leaking substantial amounts of memory, we can at least recognize the
> cause (but I suppose the dmesg will be also full of messages) and e.g. find
> the pages in a crash dump.

It might also be worth looking through the places that check
PageHWPoison() and making sure that none of them are poking into the
page contents.

It's also the kind of thing that adding some CONFIG_DEBUG_VM checks
might help with.  For instance, nobody should ever be kmap*()'ing a
private page.  The same might even go for pin_user_pages().