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Fri, 19 May 2023 08:40:50 -0700 (PDT) Date: Fri, 19 May 2023 08:40:48 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230308094106.227365-1-rppt@kernel.org> Message-ID: Subject: Re: [RFC PATCH 0/5] Prototype for direct map awareness in page allocator From: Sean Christopherson To: Mike Rapoport Cc: Rick P Edgecombe , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "peterz@infradead.org" , "tglx@linutronix.de" , "song@kernel.org" , "dave.hansen@linux.intel.com" , "vbabka@suse.cz" , "x86@kernel.org" , "akpm@linux-foundation.org" Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: 9C3C3180019 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 5uujpa1uwtmqm5i7nefmz831n1h7njkq X-HE-Tag: 1684510851-826700 X-HE-Meta: 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 AEYzeZtG 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 09, 2023, Mike Rapoport wrote: > On Thu, Mar 09, 2023 at 01:59:00AM +0000, Edgecombe, Rick P wrote: > > On Wed, 2023-03-08 at 11:41 +0200, Mike Rapoport wrote: > > > From: "Mike Rapoport (IBM)" > > > > > > Hi, > > > > > > This is a third attempt to make page allocator aware of the direct > > > map > > > layout and allow grouping of the pages that must be unmapped from > > > the direct map. > > > > > > This a new implementation of __GFP_UNMAPPED, kinda a follow up for > > > this set: > > > > > > https://lore.kernel.org/all/20220127085608.306306-1-rppt@kernel.org > > > > > > but instead of using a migrate type to cache the unmapped pages, the > > > current implementation adds a dedicated cache to serve __GFP_UNMAPPED > > > allocations. > > > > It seems a downside to having a page allocator outside of _the_ page > > allocator is you don't get all of the features that are baked in there. > > For example does secretmem care about numa? I guess in this > > implementation there is just one big cache for all nodes. > > > > Probably most users would want __GFP_ZERO. Would secretmem care about > > __GFP_ACCOUNT? > > The intention was that the pages in cache are always zeroed, so __GFP_ZERO > is always implicitly there, at least should have been. Would it be possible to drop that assumption/requirement, i.e. allow allocation of __GFP_UNMAPPED without __GFP_ZERO? At a glance, __GFP_UNMAPPED looks like it would be a great fit for backing guest memory, in particular for confidential VMs. And for some flavors of CoCo, i.e. TDX, the trusted intermediary is responsible for zeroing/initializing guest memory as the untrusted host (kernel/KVM) doesn't have access to the guest's encryption key. In other words, zeroing in the kernel would be unnecessary work.