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Mon, 12 May 2025 07:46:17 +0000 Received: from EX19D015EUB004.ant.amazon.com (10.252.51.13) by EX19D015EUB004.ant.amazon.com (10.252.51.13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1544.14; Mon, 12 May 2025 07:46:17 +0000 Received: from EX19D015EUB004.ant.amazon.com ([fe80::2dc9:7aa9:9cd3:fc8a]) by EX19D015EUB004.ant.amazon.com ([fe80::2dc9:7aa9:9cd3:fc8a%3]) with mapi id 15.02.1544.014; Mon, 12 May 2025 07:46:17 +0000 From: "Roy, Patrick" To: "david@redhat.com" CC: "ackerleytng@google.com" , "akpm@linux-foundation.org" , "amoorthy@google.com" , "anup@brainfault.org" , "aou@eecs.berkeley.edu" , "brauner@kernel.org" , "catalin.marinas@arm.com" , "chao.p.peng@linux.intel.com" , "chenhuacai@kernel.org" , "dmatlack@google.com" , "fvdl@google.com" , "hch@infradead.org" , "hughd@google.com" , "isaku.yamahata@gmail.com" , "isaku.yamahata@intel.com" , "james.morse@arm.com" , "jarkko@kernel.org" , "jgg@nvidia.com" , "jhubbard@nvidia.com" , "jthoughton@google.com" , "keirf@google.com" , "kirill.shutemov@linux.intel.com" , "kvm@vger.kernel.org" , "liam.merwick@oracle.com" , "linux-arm-msm@vger.kernel.org" , "linux-mm@kvack.org" , "mail@maciej.szmigiero.name" , "maz@kernel.org" , "mic@digikod.net" , "michael.roth@amd.com" , "mpe@ellerman.id.au" , "oliver.upton@linux.dev" , "palmer@dabbelt.com" , "pankaj.gupta@amd.com" , "paul.walmsley@sifive.com" , "pbonzini@redhat.com" , "peterx@redhat.com" , "qperret@google.com" , "quic_cvanscha@quicinc.com" , "quic_eberman@quicinc.com" , "quic_mnalajal@quicinc.com" , "quic_pderrin@quicinc.com" , "quic_pheragu@quicinc.com" , "quic_svaddagi@quicinc.com" , "quic_tsoni@quicinc.com" , "rientjes@google.com" , "Roy, Patrick" , "seanjc@google.com" , "shuah@kernel.org" , "steven.price@arm.com" , "suzuki.poulose@arm.com" , "tabba@google.com" , "vannapurve@google.com" , "vbabka@suse.cz" , "viro@zeniv.linux.org.uk" , "wei.w.wang@intel.com" , "will@kernel.org" , "willy@infradead.org" , "xiaoyao.li@intel.com" , "yilun.xu@intel.com" , "yuzenghui@huawei.com" Subject: Re: [PATCH v8 08/13] KVM: guest_memfd: Allow host to map guest_memfd() pages Thread-Topic: [PATCH v8 08/13] KVM: guest_memfd: Allow host to map guest_memfd() pages Thread-Index: AQHbwxHxVdW3j+H8JUSlmMeNB3J9nA== Date: Mon, 12 May 2025 07:46:16 +0000 Message-ID: <20250512074615.27394-1-roypat@amazon.co.uk> References: <702d9951-ac26-4ee4-8a78-d5104141c2e4@redhat.com> In-Reply-To: <702d9951-ac26-4ee4-8a78-d5104141c2e4@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [172.19.88.180] Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9271980005 X-Rspam-User: X-Stat-Signature: jgkkm8a8n49iuo35ps5tkgr6r5wuc4ed X-HE-Tag: 1747035981-212212 X-HE-Meta: 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 t1GaNKOP 4mXH9Mo2FMoU3dXJ7RikA70C6NGpxkzY6XivtPkh8V4+xQslysJh/+WavfdHg03MM9J9VQ0burRrVTNtCWcBwk2Xf3SJ/26cnRvALbyQbx5NgnvVIDZ4g08vCv6p53kz1Sdqn3AlkQI6lK2IwdNbrsUtkgprpKQ6uUEGW38zjeDB2YNKJYQjgQXgIlOiD86YeM5JllBznhVZr3EYwWz993TWgHe9Z4aHEvLz6Ejb4hZwUIvU+kU9vBMWoPr1Ts2T4SR4xUfMbvAIh9R7YFj8CXWDGYuiPnRfa1hFKFcvyMAvn/BIQuWE4OSeVcP6UndpvVEie+KZmeeCKqLkKWtlLLR9MD0ohPe+buZREVde/IVmve+yf87rXBf8VIe34EdDRnEPYLLOVwwkA74wXaLiVl/ljDSIPwjDPm10X 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: List-Subscribe: List-Unsubscribe: On Sun, 2025-05-11 at 09:03 +0100, David Hildenbrand wrote:=0A= >>> return -ENODEV;=0A= >>> +=0A= >>> + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) !=3D=0A= >>> + (VM_SHARED | VM_MAYSHARE)) {=0A= >>> + return -EINVAL;=0A= >>> + }=0A= >>> +=0A= >>> + vm_flags_set(vma, VM_DONTDUMP);=0A= >>=0A= >> Hi Fuad,=0A= >>=0A= >> Sorry if I missed this, but why exactly do we set VM_DONTDUMP here?=0A= >> Could you leave a small comment? (I see that it seems to have=0A= >> originally come from Patrick? [1]) I get that guest memory VMAs=0A= >> generally should have VM_DONTDUMP; is there a bigger reason?=0A= =0A= Iirc, I essentially copied my mmap handler from secretmem for that RFC. But= =0A= even for direct map removal, it seems this is not needed, because get_dump_= page=0A= goes via GUP, which errors out for direct map removed VMAs. So what David i= s=0A= saying below also applies in that case.=0A= =0A= > (David replying)=0A= > =0A= > I assume because we might have inaccessible parts in there that SIGBUS=0A= > on access.=0A= > =0A= > get_dump_page() does ignore any errors, though (returning NULL), so=0A= > likely we don't need VM_DONTDUMP.=0A= > =0A= > -- =0A= > Cheers,=0A= > =0A= > David / dhildenb=0A= =0A= Best,=0A= Patrick=0A=