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X-IronPort-AV: E=McAfee;i="6500,9779,10565"; a="381520282" X-IronPort-AV: E=Sophos;i="5.96,255,1665471600"; d="scan'208";a="381520282" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Dec 2022 23:57:41 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10565"; a="650470073" X-IronPort-AV: E=Sophos;i="5.96,255,1665471600"; d="scan'208";a="650470073" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga002.jf.intel.com with ESMTP; 18 Dec 2022 23:57:29 -0800 Date: Mon, 19 Dec 2022 15:53:13 +0800 From: Chao Peng To: "Huang, Kai" Cc: "linux-api@vger.kernel.org" , "linux-mm@kvack.org" , "qemu-devel@nongnu.org" , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-doc@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "tglx@linutronix.de" , "jmattson@google.com" , "Lutomirski, Andy" , "pbonzini@redhat.com" , "ak@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "david@redhat.com" , "tabba@google.com" , "Hocko, Michal" , "michael.roth@amd.com" , "corbet@lwn.net" , "bfields@fieldses.org" , "dhildenb@redhat.com" , "x86@kernel.org" , "bp@alien8.de" , "vannapurve@google.com" , "rppt@kernel.org" , "shuah@kernel.org" , "vkuznets@redhat.com" , "vbabka@suse.cz" , "arnd@arndb.de" , "mail@maciej.szmigiero.name" , "qperret@google.com" , "Christopherson,, Sean" , "ddutile@redhat.com" , "naoya.horiguchi@nec.com" , "aarcange@redhat.com" , "wanpengli@tencent.com" , "yu.c.zhang@linux.intel.com" , "hughd@google.com" , "mingo@redhat.com" , "hpa@zytor.com" , "Nakajima, Jun" , "jlayton@kernel.org" , "joro@8bytes.org" , "steven.price@arm.com" , "Hansen, Dave" , "akpm@linux-foundation.org" , "linmiaohe@huawei.com" , "Wang, Wei W" Subject: Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory Message-ID: <20221219075313.GB1691829@chaop.bj.intel.com> Reply-To: Chao Peng References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com> <20221202061347.1070246-2-chao.p.peng@linux.intel.com> <5c6e2e516f19b0a030eae9bf073d555c57ca1f21.camel@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5c6e2e516f19b0a030eae9bf073d555c57ca1f21.camel@intel.com> X-Rspamd-Queue-Id: 1387E140006 X-Stat-Signature: 6upt7cq9jpuwid6idya9cyqs1dqywt5g X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1671436664-444849 X-HE-Meta: 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 191Zv4/K /Evi6EON1aI/BZ6QhDZopX8z/RA4ZGQVKP7+RcJ5evmibNYRx+dJTQ6ucfrkdL8/1U488 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 Tue, Dec 13, 2022 at 11:49:13PM +0000, Huang, Kai wrote: > > > > memfd_restricted() itself is implemented as a shim layer on top of real > > memory file systems (currently tmpfs). Pages in restrictedmem are marked > > as unmovable and unevictable, this is required for current confidential > > usage. But in future this might be changed. > > > > > I didn't dig full histroy, but I interpret this as we don't support page > migration and swapping for restricted memfd for now. IMHO "page marked as > unmovable" can be confused with PageMovable(), which is a different thing from > this series. It's better to just say something like "those pages cannot be > migrated and swapped". Yes, if that helps some clarification. > > [...] > > > + > > + /* > > + * These pages are currently unmovable so don't place them into movable > > + * pageblocks (e.g. CMA and ZONE_MOVABLE). > > + */ > > + mapping = memfd->f_mapping; > > + mapping_set_unevictable(mapping); > > + mapping_set_gfp_mask(mapping, > > + mapping_gfp_mask(mapping) & ~__GFP_MOVABLE); > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from non- > movable zones, but doesn't necessarily prevent page from being migrated. My > first glance is you need to implement either a_ops->migrate_folio() or just > get_page() after faulting in the page to prevent. The current api restrictedmem_get_page() already does this, after the caller calling it, it holds a reference to the page. The caller then decides when to call put_page() appropriately. > > So I think the comment also needs improvement -- IMHO we can just call out > currently those pages cannot be migrated and swapped, which is clearer (and the > latter justifies mapping_set_unevictable() clearly). Good to me. Thanks, Chao > >