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: <01a24370-895c-465a-c7fb-0c6a86c301bc@amd.com>
Date:   Tue, 15 Nov 2022 16:44:46 -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

Hello Boris,

On 11/15/2022 10:27 AM, Borislav Petkov wrote:
> And,
> 
> as dhansen connected the dots, this should be the exact same protection
> scenario as UPM:
> 
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20221025151344.3784230-1-chao.p.peng%40linux.intel.com&amp;data=05%7C01%7Cashish.kalra%40amd.com%7Cbfecf32a51eb499b526d08dac726491e%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638041264625164355%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=3RqOC3b9qn0%2B2IRsTZURBmhAVtOn7rARR6fOMOsrFpE%3D&amp;reserved=0
> 
> so you should be able to mark them inaccessible the same way and you
> won't need any poisoning dance.

With UPM, the guest pages are all still freed back to the host after 
guest shutdown, so it's not clear how this would help with handling of 
leaked pages, for e.g, the host can still access these pages once the 
guest is shutdown and it will cause the RMP violation #PF at that point.

Additionally, our use case is of host allocated firmware pages as part 
of the crypto driver (to be passed to SNP firmware api calls
and then re-transitioned back to host state on return) so these are not 
guest private pages in the true sense and they need to be
handled differently in case there is a failure in reclaiming them.

Can you elaborate on what you have in mind ?

Thanks,
Ashish

> 
> And Michael has patches so you probably should talk to him...
> 
> Thx.
>