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bh=l7IqxgTGgOUrrRLp/9kEkeElM34tTO5S0maFth2gfks=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VF1ZxWOsDhHWaJROcCgln8Hk8HRRpZ6O1WlOpqGsQF66QGWjGTWJ9Nd1/D9UsgRIe vKUedzeZUSBtnbtv3lm0tFU5AsUwrTT6+sVq61IuhcRzdGrl0ZsyJLGpScoTfCXJJh zA7FNLg7M8o/dj/uZgSB1tGhC6Ibmoo5jD3SOjfazOqofa5udrf3iNq+BLaB8tFuR5 1fGrvop1FmSUiLwjXbquoL0VTW/G7AoWZVFrJnu3Zq5pgz5PwMeWGe93i1U8iFpgZ9 h22nqG/+VnalqFvfeQB5Rnm7Cd5gkJFPIDCaoU/OoGnH536xVCiWOLDAlLA36vlOl6 giYN9E4mPIOoA== Date: Fri, 19 May 2023 19:24:32 +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: <20230519162432.GG4967@kernel.org> References: <20230308094106.227365-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1BE6A4001B X-Stat-Signature: c7x93744qqnib15mabtd1t6h6s1qf35e X-HE-Tag: 1684513487-550156 X-HE-Meta: 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 k5Yi4gIK SvPvvf3YDATTjI4Rrjg506zczPUxcWOapBQrx7jbDtrDWVgrzxiFOnPV4IKnOKWE9ej31o61S9m1mzhKeW+QyNgSvbob05kRcuHdAUbMU4kV2PMX53t6AXesCNEy/bIdNxZpYlhC8MEnK/U+tYfhX/wkiyy56BM1LgXltnDr8R6J8gEy69ToMDvUnAH2nfVSq9QIr1IgYhxfng0clYv4LmRSiAGvSCqx3A7NivaR4pmKtAbFgpf2y0iwUayGfVF7pmTLx37/wGh2tVDhCCg6fKGAMUHFZH+noLAb5HxtZ24WW6My0WLCVIAh1wfK53zMY0s/84zNm9DF3tBiGEaED71GAghc4N9unRqFVl9mGxfD87SH7UeVCI/1H9pVieCKlWkAGyX2Mxpl3oFU= 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 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: > > > 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. 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? -- Sincerely yours, Mike.