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Wed, 10 Jul 2024 09:51:21 +0000 Received: from EX19MTAUEA001.ant.amazon.com (10.252.134.203) by EX19D008UEA003.ant.amazon.com (10.252.134.116) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.34; Wed, 10 Jul 2024 09:51:20 +0000 Received: from [127.0.0.1] (172.19.88.180) by mail-relay.amazon.com (10.252.134.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.34 via Frontend Transport; Wed, 10 Jul 2024 09:51:18 +0000 Message-ID: Date: Wed, 10 Jul 2024 10:51:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: David Hildenbrand , Fuad Tabba CC: , , , , , , , , , , , , , , , , , , , , , James Gowans References: <20240709132041.3625501-1-roypat@amazon.co.uk> <20240709132041.3625501-9-roypat@amazon.co.uk> <47ce1b10-e031-4ac1-b88f-9d4194533745@redhat.com> Content-Language: en-US From: Patrick Roy Autocrypt: addr=roypat@amazon.co.uk; keydata= xjMEY0UgYhYJKwYBBAHaRw8BAQdA7lj+ADr5b96qBcdINFVJSOg8RGtKthL5x77F2ABMh4PN NVBhdHJpY2sgUm95IChHaXRodWIga2V5IGFtYXpvbikgPHJveXBhdEBhbWF6b24uY28udWs+ wpMEExYKADsWIQQ5DAcjaM+IvmZPLohVg4tqeAbEAgUCY0UgYgIbAwULCQgHAgIiAgYVCgkI CwIEFgIDAQIeBwIXgAAKCRBVg4tqeAbEAmQKAQC1jMl/KT9pQHEdALF7SA1iJ9tpA5ppl1J9 AOIP7Nr9SwD/fvIWkq0QDnq69eK7HqW14CA7AToCF6NBqZ8r7ksi+QLOOARjRSBiEgorBgEE AZdVAQUBAQdAqoMhGmiXJ3DMGeXrlaDA+v/aF/ah7ARbFV4ukHyz+CkDAQgHwngEGBYKACAW IQQ5DAcjaM+IvmZPLohVg4tqeAbEAgUCY0UgYgIbDAAKCRBVg4tqeAbEAtjHAQDkh5jZRIsZ 7JMNkPMSCd5PuSy0/Gdx8LGgsxxPMZwePgEAn5Tnh4fVbf00esnoK588bYQgJBioXtuXhtom 8hlxFQM= In-Reply-To: <47ce1b10-e031-4ac1-b88f-9d4194533745@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Stat-Signature: 8a1gczp9maoibna6r9p8c15wg66nq55x X-Rspamd-Queue-Id: 793241C0016 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1720605102-715982 X-HE-Meta: U2FsdGVkX1/atInMBiRqU8DBSjRAdU2rZGFYWW9sDX9IFbURyFWUUItH6iNXvV5KXVeAawgAB8jKItlr7M+Rxzluo4CJ8qO4EkY1DoNCgXOOBz1PZGOMLf4hX1Rok/sXgHMjuNxfWvsWPUt4aEwvvj4qQ4wLm9P3nioRVwYJYecVXUhv8yjjhRscCjkkk4/tZVsDpVqJkwsRNPuanvfgLxxGaEy9sMVr5mbkGrj1JmhPmcaX2oWlWnAd0HGCCLrRL5j4CshNgB8jQTPyM6IaZNsGYlvOiDTyJf8D2MgGD2+k7aG+KiOY4hI1cxlOnYgfeEl1dAU6zFJhrkPyfpeHelqGaiyEGfKNoDOwyUvbkq4xkGN5DcjqTXjT0a62s8B3zIjZvIdR3sK48UNULF/o6u6JVE1ePLqvo75kfn/ghsyxXDAjcIc3CunLS2qeB12xsoL6LtGh+UwKxLwlQqh1IFL0A50B/3qWZHzLZrWgKzXKjbS/k7eCmiNyUGkSyBRb3bhvdKTtSYCL8qprtii50jXLIw6Nc05/AUrKfN/Vj9EqmfOFMSa86LaDsVluDXKMtgqswnOkprfHKSoWOLrmcAv9GLYpBXsrhHOCalvGoxR2YaOzVsUpFT1lpMkL8qm5/tR/jY5m5hCHDT3gehIP5Wscqk6rFk/oKR7wUudGZvtX6X5qEy033VLtHCGTnfoZZDt5+G3SfJrFqklTxfZsAAosycWPX3GgJqVdzlhtGbb6Vmf8jIHazKanBkjcHHQd0N3mSR6ZpbCJUcIqgrJiuY1Vgnr6XcAV9u0iPmJG47oFhS/F4BGD2X4qZoY2S3X0PPfDybIcfvMH1yM/Yro68LGjDnlFtKbNYZDwFbB43O1uhjD5iBMH3TPgle/D+ibtuzrcUZRUsyWfXOzJ5yjDz+2ioQxflJBhAXh2NjmA70/oc3+89T1zCiOQc26UyM2BNY547xrvqeCvuN5oXxT trMIDzCp 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 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 7/9/24 22:13, David Hildenbrand wrote: > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > On 09.07.24 16:48, Fuad Tabba wrote: >> Hi Patrick, >> >> On Tue, Jul 9, 2024 at 2:21 PM Patrick Roy wrote: >>> >>> Allow mapping guest_memfd into userspace. Since AS_INACCESSIBLE is set >>> on the underlying address_space struct, no GUP of guest_memfd will be >>> possible. >> >> This patch allows mapping guest_memfd() unconditionally. Even if it's >> not guppable, there are other reasons why you wouldn't want to allow >> this. Maybe a config flag to gate it? e.g., > > > As discussed with Jason, maybe not the direction we want to take with > guest_memfd. > If it's private memory, it shall not be mapped. Also not via magic > config options. > > We'll likely discuss some of that in the meeting MM tomorrow I guess > (having both shared and private memory in guest_memfd). Oh, nice. I'm assuming you mean this meeting: https://lore.kernel.org/linux-mm/197a2f19-c71c-fbde-a62a-213dede1f4fd@google.com/T/? Would it be okay if I also attend? I see it also mentions huge pages, which is another thing we are interested in, actually :) > Note that just from staring at this commit, I don't understand the > motivation *why* we would want to do that. Fair - I admittedly didn't get into that as much as I probably should have. In our usecase, we do not have anything that pKVM would (I think) call "guest-private" memory. I think our memory can be better described as guest-owned, but always shared with the VMM (e.g. userspace), but ideally never shared with the host kernel. This model lets us do a lot of simplifying assumptions: Things like I/O can be handled in userspace without the guest explicitly sharing I/O buffers (which is not exactly what we would want long-term anyway, as sharing in the guest_memfd context means sharing with the host kernel), we can easily do VM snapshotting without needing things like TDX's TDH.EXPORT.MEM APIs, etc. > -- > Cheers, > > David / dhildenb >