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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 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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