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Date:   Fri, 8 Apr 2022 21:04:16 +0200
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Subject: Re: [PATCHv4 1/8] mm: Add support for unaccepted memory
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To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>
Cc:     Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Varad Gautam <varad.gautam@suse.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Mike Rapoport <rppt@kernel.org>, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mike Rapoport <rppt@linux.ibm.com>
References: <20220405234343.74045-1-kirill.shutemov@linux.intel.com>
 <20220405234343.74045-2-kirill.shutemov@linux.intel.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20220405234343.74045-2-kirill.shutemov@linux.intel.com>
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On 06.04.22 01:43, Kirill A. Shutemov wrote:
> UEFI Specification version 2.9 introduces the concept of memory
> acceptance. Some Virtual Machine platforms, such as Intel TDX or AMD
> SEV-SNP, requiring memory to be accepted before it can be used by the
> guest. Accepting happens via a protocol specific for the Virtual Machine
> platform.
> 
> Accepting memory is costly and it makes VMM allocate memory for the
> accepted guest physical address range. It's better to postpone memory
> acceptance until memory is needed. It lowers boot time and reduces
> memory overhead.
> 
> Support of such memory requires a few changes in core-mm code:
> 
>   - memblock has to accept memory on allocation;
> 
>   - page allocator has to accept memory on the first allocation of the
>     page;
> 
> Memblock change is trivial.
> 
> The page allocator is modified to accept pages on the first allocation.
> PageUnaccepted() is used to indicate that the page requires acceptance.
> 
> Kernel only needs to accept memory once after boot, so during the boot
> and warm up phase there will be a lot of memory acceptance. After things
> are settled down the only price of the feature if couple of checks for
> PageUnaccepted() in allocate and free paths. The check refers a hot
> variable (that also encodes PageBuddy()), so it is cheap and not visible
> on profiles.
> 
> Architecture has to provide two helpers if it wants to support
> unaccepted memory:
> 
>  - accept_memory() makes a range of physical addresses accepted.
> 
>  - memory_is_unaccepted() checks anything within the range of physical
>    addresses requires acceptance.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Acked-by: Mike Rapoport <rppt@linux.ibm.com>	# memblock

Thanks, I skimmed over most parts and nothing obvious jumped at me. Dave
has some good suggestions; I'll try giving it a thorough in the near future.


-- 
Thanks,

David / dhildenb