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[2003:cb:c707:2400:68a3:92e0:906f:b69d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4316067dbedsm19713015e9.7.2024.10.18.00.50.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Oct 2024 00:50:50 -0700 (PDT) Message-ID: <257d5578-f256-49cf-affe-6255ff224ed0@redhat.com> Date: Fri, 18 Oct 2024 09:50:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a struct kvm_gmem_private To: Patrick Roy , Jason Gunthorpe , Peter Xu Cc: Ackerley Tng , tabba@google.com, quic_eberman@quicinc.com, rientjes@google.com, fvdl@google.com, jthoughton@google.com, seanjc@google.com, pbonzini@redhat.com, zhiquan1.li@intel.com, fan.du@intel.com, jun.miao@intel.com, isaku.yamahata@intel.com, muchun.song@linux.dev, erdemaktas@google.com, vannapurve@google.com, qperret@google.com, jhubbard@nvidia.com, willy@infradead.org, shuah@kernel.org, brauner@kernel.org, bfoster@redhat.com, kent.overstreet@linux.dev, pvorel@suse.cz, rppt@kernel.org, richard.weiyang@gmail.com, anup@brainfault.org, haibo1.xu@intel.com, ajones@ventanamicro.com, vkuznets@redhat.com, maciej.wieczor-retman@intel.com, pgonda@google.com, oliver.upton@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <1d243dde-2ddf-4875-890d-e6bb47931e40@redhat.com> <20241016225157.GQ3559746@nvidia.com> <20241016235424.GU3559746@nvidia.com> <20241017164713.GF3559746@nvidia.com> <20241017171010.GK3559746@nvidia.com> <20241017191829.GA3559746@nvidia.com> <2686a5ae-e1e5-48d6-ae4b-31face5284ca@amazon.co.uk> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 628FA180003 X-Stat-Signature: s96bhfb4ebygacornw17ndm178szrnga X-HE-Tag: 1729237855-802410 X-HE-Meta: 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 qcNZTrhr 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 18.10.24 09:15, Patrick Roy wrote: > > > On Thu, 2024-10-17 at 20:18 +0100, Jason Gunthorpe wrote: >> On Thu, Oct 17, 2024 at 03:11:10PM -0400, Peter Xu wrote: >>> On Thu, Oct 17, 2024 at 02:10:10PM -0300, Jason Gunthorpe wrote: >>>>> If so, maybe that's a non-issue for non-CoCo, where the VM object / >>>>> gmemfd object (when created) can have a flag marking that it's >>>>> always shared and can never be converted to private for any page >>>>> within. >>>> >>>> What is non-CoCo? Does it include the private/shared concept? >>> >>> I used that to represent the possible gmemfd use cases outside confidential >>> computing. >>> >>> So the private/shared things should still be around as fundamental property >>> of gmemfd, but it should be always shared and no convertion needed for the >>> whole lifecycle of the gmemfd when marked !CoCo. >> >> But what does private mean in this context? >> >> Is it just like a bit of additional hypervisor security that the page >> is not mapped anyplace except the KVM stage 2 and the hypervisor can >> cause it to become mapped/shared at any time? But the guest has no >> idea about this? >> >> Jason > > Yes, this is pretty much exactly what I'm after when I say "non-CoCo". It's likely not what Peter meant, though. I think there are three scenarios: (a) Secure CoCo VMs: private is protected by HW (b) Semi-secured non-CoCo VMs: private is removed from the directmap (c) Non-CoCo VMs: only shared memory Does that match what you have in mind? Are there other cases? -- Cheers, David / dhildenb