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s=k20201202; t=1685047083; bh=i51ujcjCkUGno5zWuS49FNmOut45twOgb5SnLa+ZZd8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jU+t0T6qn2GOdIktSugYG53391Zm3n4pxwTLlVTiRwYvcvW9HxM1M/Z/Apdm7A/3x RhAv58JX29uv52ZLGe5PgOvtn/StubGB6Rq5TqGIj2yw0GSVtdhjq2pxejX/EOqClm 39AtplVtdn4OIlnOE0FZB/G+3Top3BI+zmUeqo+2kPd7wqNuqy2zv6LuQsegIqNupT COmDqMtNP8muGmiiTePMUv2Yfilf1kj+WkRAPuLjedgbZBskYdL0vI5TKvPx0jbBaw +HiagTP13tMhcPp4b/xLdwKnTZJYoHnWNxup5ZE+cdXcfXGuNuyj9Q9tt9NxOuhJrF /LyK/49+ix26w== Date: Thu, 25 May 2023 23:37:40 +0300 From: Mike Rapoport To: Sean Christopherson 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" Subject: Re: [RFC PATCH 0/5] Prototype for direct map awareness in page allocator Message-ID: <20230525203740.GB4967@kernel.org> References: <20230308094106.227365-1-rppt@kernel.org> <20230519162432.GG4967@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 0385EC0007 X-Rspam-User: X-Stat-Signature: 5g4iqxqf6jhwzodgwxf13q6o5w7csfqa X-Rspamd-Server: rspam03 X-HE-Tag: 1685047083-118672 X-HE-Meta: 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 +aDGTpLQ k2u75vr7WhovLv+rJ2IW0KJlcRdr1XnUNc38dJ0jTlbxJai1CZFJ+iz0KEczRqGm6rBm/IY3EBFliaAfH0qesPN9F0Asl9oXnkaVq+8dUjYYVT/m7qODqT7YYX1ShP9nPUF/6WguHVcC66a+RrqVkygOnoOuvbAPXRFEU8zTCtku2bR7XnW62OUhdV/6/6rReHQil6KPNI3jCI9S6L1roV2VqETP7VeZEd1/RiwauunTdMWF4siTy3tv/4A7KAItt9uUAFTaotEb0XOBv6GXap9htsfGPyp3aMjSnW498DOKeMNFJkwyr5I8LrdTef0sX8PDUEtNcjWoj68q3+W2gBEdg84s32GK/wEO7tGhJIkcyQvhqWb+rjgk/fV9RQvQlzTJ6fw0inDuhiJI= 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 Fri, May 19, 2023 at 11:25:53AM -0700, Sean Christopherson wrote: > On Fri, May 19, 2023, Mike Rapoport wrote: > > On Fri, May 19, 2023 at 08:40:48AM -0700, Sean Christopherson wrote: > > > On Thu, Mar 09, 2023, Mike Rapoport wrote: > > > > On Thu, Mar 09, 2023 at 01:59:00AM +0000, Edgecombe, Rick P wrote: > > > > > > 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. > > > > Making and unmapped allocation without __GFP_ZERO shouldn't be a problem. > > > > However, using a gfp flag and hooking up into the free path in page > > allocator have issues and preferably should be avoided. > > > > Will something like unmapped_alloc() and unmapped_free() work for your > > usecase? > > Yep, I'm leaning more and more towards having KVM implement its own ioctl() for > managing this type of memory. Wiring that up to use dedicated APIs should be no > problem. Ok, I've dropped the GFP flag and made unmapped_pages_{alloc,free} the only APIs. Totally untested version of what I've got is here: https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=unmapped-alloc/rfc-v2 I have some thoughts about adding support for 1G pages, but this is still really vague at the moment. > Thanks! -- Sincerely yours, Mike.