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Date:   Wed, 16 Nov 2022 12:53:36 -0600
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Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled
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To:     Borislav Petkov <bp@alien8.de>
Cc:     Vlastimil Babka <vbabka@suse.cz>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com,
        ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com,
        vkuznets@redhat.com, jmattson@google.com, luto@kernel.org,
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        michael.roth@amd.com, kirill@shutemov.name, ak@linux.intel.com,
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        "Kaplan, David" <David.Kaplan@amd.com>,
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From:   "Kalra, Ashish" <ashish.kalra@amd.com>
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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.
>