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 12:53:36 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Vlastimil Babka <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,
        "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 11/16/2022 12:33 PM, Borislav Petkov wrote:
> On Wed, Nov 16, 2022 at 12:01:11PM -0600, Kalra, Ashish wrote:
>> Ok, so i will work on implementing this leaked pages list and put it on a
>> sev/snp associated structure.
> 
> See __sgx_sanitize_pages() and the poison list there, for an example.
> 
>> Also to add here, we will actually get a not-present #PF instead of the RMP
>> violation #PF on writing to these leaked pages, as these pages would have
>> been removed from the kernel direct map.
> 
> So if you do the list and still have the kernel raise a RMP fault for
> those pages, traversing that list in the RMP handler to check whether
> the page is there on it, should be a lot faster operation than doing the
> #PF thing and removing them from the direct map.
> 

Actually, these host allocated pages would have already been removed 
from the kernel direct map, when they were transitioned to the firmware 
state. So actually the not-present #PF fault will happen on any 
read/write access to these leaked pages instead of the RMP violation #PF 
(not-present #PF has higher priority than RMP violation #PF).

If these pages cannot be reclaimed, they are unsafe to use and cannot be 
added back to the kernel direct map.

Thanks,
Ashish

> And sorry for misleading you about UPM - we were thinking wrong
> yesterday.
> 
> Thx.
>