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X-CSE-ConnectionGUID: /sD8iGQfSgSVn7His97m2w== X-CSE-MsgGUID: thxXek9eQo6j2MEfNEt7FQ== X-IronPort-AV: E=McAfee;i="6800,10657,11633"; a="92471070" X-IronPort-AV: E=Sophos;i="6.20,252,1758610800"; d="scan'208";a="92471070" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Dec 2025 09:30:13 -0800 X-CSE-ConnectionGUID: 0zVgGn7kRryd4YRQDDxvpw== X-CSE-MsgGUID: JpgCbNWPR9SJGQ2HiyIx1Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.20,252,1758610800"; d="scan'208";a="232715651" Received: from vverma7-desk1.amr.corp.intel.com (HELO [10.125.108.173]) ([10.125.108.173]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Dec 2025 09:30:11 -0800 Message-ID: <51a059a1-f03a-4b43-8df6-d31fca09cce7@intel.com> Date: Fri, 5 Dec 2025 09:30:09 -0800 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 05/13] KVM: guest_memfd: Add flag to remove from direct map To: "Kalyazin, Nikita" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" 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" , "baohua@kernel.org" , "ryan.roberts@arm.com" , "jgross@suse.com" , "yu-cheng.yu@intel.com" , "kas@kernel.org" , "coxu@redhat.com" , "kevin.brodsky@arm.com" , "ackerleytng@google.com" , "maobibo@loongson.cn" , "prsampat@amd.com" , "mlevitsk@redhat.com" , "isaku.yamahata@intel.com" , "jmattson@google.com" , "jthoughton@google.com" , "linux-arm-kernel@lists.infradead.org" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" , "Cali, Marco" References: <20251205165743.9341-1-kalyazin@amazon.com> <20251205165743.9341-6-kalyazin@amazon.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/5/25 08:58, Kalyazin, Nikita wrote: > +static void kvm_gmem_folio_restore_direct_map(struct folio *folio) > +{ > + /* > + * Direct map restoration cannot fail, as the only error condition > + * for direct map manipulation is failure to allocate page tables > + * when splitting huge pages, but this split would have already > + * happened in set_direct_map_invalid_noflush() in kvm_gmem_folio_zap_direct_map(). > + * Thus set_direct_map_valid_noflush() here only updates prot bits. > + */ > + if (kvm_gmem_folio_no_direct_map(folio)) > + set_direct_map_valid_noflush(folio_page(folio, 0), folio_nr_pages(folio), > + true); > +} This is rather hopeful programming. I can think of a number of ways that this assumption might become invalid. This at *least* check for set_direct_map_valid_noflush() failures (or whatever interface you end up using)? A WARN_ON_ONCE() would be fine.