From: Sean Christopherson <seanjc@google.com>
To: Vishal Annapurve <vannapurve@google.com>
Cc: Xiaoyao Li <xiaoyao.li@intel.com>, Fuad Tabba <tabba@google.com>,
kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org,
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Subject: Re: [PATCH v15 14/21] KVM: x86: Enable guest_memfd mmap for default VM type
Date: Wed, 23 Jul 2025 07:43:50 -0700 [thread overview]
Message-ID: <aID1JoOGRZ8HIkc9@google.com> (raw)
In-Reply-To: <CAGtprH8QfPU8tByPLHL69MOhG5hNspS6zCjxzB8xM_Tbjgcs1w@mail.gmail.com>
On Wed, Jul 23, 2025, Vishal Annapurve wrote:
> 2) Userspace brings a mappable guest_memfd to back guest private
> memory (passed as guest_memfd field in the
> KVM_USERSPACE_MEMORY_REGION2): KVM will always fault in all guest
> faults via guest_memfd so if userspace brings in VMAs that point to
> different physical memory then there would be a discrepancy between
> what guest and userspace/KVM (going through HVAs) sees for shared
> memory ranges. I am not sure if KVM needs to enforce anything here,
We agreed (I think in a guest_memfd call?) that KVM won't enforce anything,
because trying to do so for uaccesses, e.g. via __kvm_read_guest_page(), would
require grabbing mmap_lock in hot paths, i.e. would be a complete non-starter.
So yeah, it's the VMM's responsibility to not be stupid.
next prev parent reply other threads:[~2025-07-23 14:43 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-17 16:27 [PATCH v15 00/21] KVM: Enable host userspace mapping for guest_memfd-backed memory for non-CoCo VMs Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 01/21] KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GMEM Fuad Tabba
2025-07-21 15:17 ` Sean Christopherson
2025-07-21 15:26 ` Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 02/21] KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to CONFIG_KVM_GENERIC_GMEM_POPULATE Fuad Tabba
2025-07-21 16:44 ` Sean Christopherson
2025-07-21 16:51 ` Fuad Tabba
2025-07-21 17:33 ` Sean Christopherson
2025-07-22 9:29 ` Fuad Tabba
2025-07-22 15:58 ` Sean Christopherson
2025-07-22 16:01 ` Fuad Tabba
2025-07-22 23:42 ` Sean Christopherson
2025-07-23 9:22 ` Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 03/21] KVM: Introduce kvm_arch_supports_gmem() Fuad Tabba
2025-07-18 1:42 ` Xiaoyao Li
2025-07-21 14:47 ` Sean Christopherson
2025-07-21 14:55 ` Fuad Tabba
2025-07-21 16:44 ` Sean Christopherson
2025-07-17 16:27 ` [PATCH v15 04/21] KVM: x86: Introduce kvm->arch.supports_gmem Fuad Tabba
2025-07-21 16:45 ` Sean Christopherson
2025-07-21 17:00 ` Fuad Tabba
2025-07-21 19:09 ` Sean Christopherson
2025-07-17 16:27 ` [PATCH v15 05/21] KVM: Rename kvm_slot_can_be_private() to kvm_slot_has_gmem() Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 06/21] KVM: Fix comments that refer to slots_lock Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 07/21] KVM: Fix comment that refers to kvm uapi header path Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 08/21] KVM: guest_memfd: Allow host to map guest_memfd pages Fuad Tabba
2025-07-18 2:56 ` Xiaoyao Li
2025-07-17 16:27 ` [PATCH v15 09/21] KVM: guest_memfd: Track guest_memfd mmap support in memslot Fuad Tabba
2025-07-18 3:33 ` Xiaoyao Li
2025-07-17 16:27 ` [PATCH v15 10/21] KVM: x86/mmu: Generalize private_max_mapping_level x86 op to max_mapping_level Fuad Tabba
2025-07-18 6:19 ` Xiaoyao Li
2025-07-21 19:46 ` Sean Christopherson
2025-07-17 16:27 ` [PATCH v15 11/21] KVM: x86/mmu: Allow NULL-able fault in kvm_max_private_mapping_level Fuad Tabba
2025-07-18 5:10 ` Xiaoyao Li
2025-07-21 23:17 ` Sean Christopherson
2025-07-22 5:35 ` Xiaoyao Li
2025-07-22 11:08 ` Fuad Tabba
2025-07-22 14:32 ` Sean Christopherson
2025-07-22 15:30 ` Fuad Tabba
2025-07-22 10:35 ` Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 12/21] KVM: x86/mmu: Consult guest_memfd when computing max_mapping_level Fuad Tabba
2025-07-18 5:32 ` Xiaoyao Li
2025-07-18 5:57 ` Xiaoyao Li
2025-07-17 16:27 ` [PATCH v15 13/21] KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory Fuad Tabba
2025-07-18 6:09 ` Xiaoyao Li
2025-07-21 16:47 ` Sean Christopherson
2025-07-21 16:56 ` Fuad Tabba
2025-07-22 5:41 ` Xiaoyao Li
2025-07-22 8:43 ` Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 14/21] KVM: x86: Enable guest_memfd mmap for default VM type Fuad Tabba
2025-07-18 6:10 ` Xiaoyao Li
2025-07-21 12:22 ` Xiaoyao Li
2025-07-21 12:41 ` Fuad Tabba
2025-07-21 13:45 ` Vishal Annapurve
2025-07-21 14:42 ` Xiaoyao Li
2025-07-21 14:42 ` Sean Christopherson
2025-07-21 15:07 ` Xiaoyao Li
2025-07-21 17:29 ` Sean Christopherson
2025-07-21 20:33 ` Vishal Annapurve
2025-07-21 22:21 ` Sean Christopherson
2025-07-21 23:50 ` Vishal Annapurve
2025-07-22 14:35 ` Sean Christopherson
2025-07-23 14:08 ` Vishal Annapurve
2025-07-23 14:43 ` Sean Christopherson [this message]
2025-07-23 14:46 ` David Hildenbrand
2025-07-22 14:28 ` Xiaoyao Li
2025-07-22 14:37 ` Sean Christopherson
2025-07-22 15:31 ` Xiaoyao Li
2025-07-22 15:50 ` David Hildenbrand
2025-07-22 15:54 ` Sean Christopherson
2025-07-17 16:27 ` [PATCH v15 15/21] KVM: arm64: Refactor user_mem_abort() Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 16/21] KVM: arm64: Handle guest_memfd-backed guest page faults Fuad Tabba
2025-07-22 12:31 ` Kunwu Chan
2025-07-23 8:20 ` Marc Zyngier
2025-07-23 11:44 ` Kunwu Chan
2025-07-23 8:26 ` Marc Zyngier
2025-07-17 16:27 ` [PATCH v15 17/21] KVM: arm64: nv: Handle VNCR_EL2-triggered faults backed by guest_memfd Fuad Tabba
2025-07-23 8:29 ` Marc Zyngier
2025-07-17 16:27 ` [PATCH v15 18/21] KVM: arm64: Enable host mapping of shared guest_memfd memory Fuad Tabba
2025-07-23 8:33 ` Marc Zyngier
2025-07-23 9:18 ` Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 19/21] KVM: Introduce the KVM capability KVM_CAP_GMEM_MMAP Fuad Tabba
2025-07-18 6:14 ` Xiaoyao Li
2025-07-21 17:31 ` Sean Christopherson
2025-07-17 16:27 ` [PATCH v15 20/21] KVM: selftests: Do not use hardcoded page sizes in guest_memfd test Fuad Tabba
2025-07-17 16:27 ` [PATCH v15 21/21] KVM: selftests: guest_memfd mmap() test when mmap is supported Fuad Tabba
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