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Thu, 22 Jan 2026 20:40:52 +0000 (UTC) X-Farcaster-Flow-ID: a5dd7989-855e-4510-b2e9-5fd9107a3c02 Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUA001.ant.amazon.com (10.252.50.50) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Thu, 22 Jan 2026 20:40:51 +0000 Received: from [192.168.23.186] (10.106.82.17) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Thu, 22 Jan 2026 20:40:47 +0000 Message-ID: <0635e64a-2194-4a6c-b772-28af54d58e3b@amazon.com> Date: Thu, 22 Jan 2026 20:40:46 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct map To: Ackerley Tng , "Kalyazin, Nikita" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "kernel@xen0n.name" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "loongarch@lists.linux.dev" CC: "pbonzini@redhat.com" , "corbet@lwn.net" , "maz@kernel.org" , "oupton@kernel.org" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "seanjc@google.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "luto@kernel.org" , "peterz@infradead.org" , "willy@infradead.org" , "akpm@linux-foundation.org" , "david@kernel.org" , "lorenzo.stoakes@oracle.com" , "Liam.Howlett@oracle.com" , "vbabka@suse.cz" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "song@kernel.org" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jolsa@kernel.org" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "shuah@kernel.org" , "riel@surriel.com" , "ryan.roberts@arm.com" , "jgross@suse.com" , "yu-cheng.yu@intel.com" , "kas@kernel.org" , "coxu@redhat.com" , "kevin.brodsky@arm.com" , "maobibo@loongson.cn" , "prsampat@amd.com" , "mlevitsk@redhat.com" , "jmattson@google.com" , "jthoughton@google.com" , "agordeev@linux.ibm.com" , "alex@ghiti.fr" , "aou@eecs.berkeley.edu" , "borntraeger@linux.ibm.com" , "chenhuacai@kernel.org" , "dev.jain@arm.com" , "gor@linux.ibm.com" , "hca@linux.ibm.com" , "Jonathan.Cameron@huawei.com" , "palmer@dabbelt.com" , "pjw@kernel.org" , "shijie@os.amperecomputing.com" , "svens@linux.ibm.com" , "thuth@redhat.com" , "wyihan@google.com" , "yang@os.amperecomputing.com" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" , "Cali, Marco" References: <20260114134510.1835-1-kalyazin@amazon.com> <20260114134510.1835-8-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; 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>>>>>> int order = folio_order(folio); >>>>>> >>>>>> + kvm_gmem_folio_restore_direct_map(folio); >>>>>> + >>>>> >>>>> I can't decide if the kvm_gmem_folio_no_direct_map(folio) should be in >>>>> the caller or within kvm_gmem_folio_restore_direct_map(), since this >>>>> time it's a folio-specific property being checked. >>>> >>>> I'm tempted to keep it similar to the kvm_gmem_folio_zap_direct_map() >>>> case. How does the fact it's a folio-speicific property change your >>>> reasoning? >>>> >>> >>> This is good too: >>> >>> if (kvm_gmem_folio_no_direct_map(folio)) >>> kvm_gmem_folio_restore_direct_map(folio) >> >> It turns out we can't do that because folio->mapping is gone by the time >> filemap_free_folio() is called so we can't inspect the flags. Are you >> ok with only having this check when zapping (but not when restoring)? >> Do you think we should add a comment saying it's conditional here? >> > > I thought kvm_gmem_folio_no_direct_map() only reads folio->private, > which I think should still be there at the point of > filemap_free_folio(). Oh, I misread your last reply. What you're proposing would work indeed. > >>> >>> [...snip...] >>>