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quic_eberman@quicinc.com, roypat@amazon.co.uk, 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 Subject: Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a struct kvm_gmem_private Message-ID: <20241017171010.GK3559746@nvidia.com> References: <1d243dde-2ddf-4875-890d-e6bb47931e40@redhat.com> 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fd+offsets yet. > > > > I keep hearing they don't want to support page pinning on a guestmemfd > > mapping, so VA based paths could not work. > > Do you remember the reasoning of it? Is it because CoCo still needs to > have a bounded time window to convert from shared back to private? I think so > 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? > So how would VFIO's DMA work even with iommufd if pages cannot be pinned? > Is some form of bounce buffering required, then? We can do some kind of atomic replace during a private/shared exchange. In some HW cases the iommu table doesn't even need an update. It will be tricky stuff. Jason