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Wed, 21 May 2025 01:25:33 -0700 (PDT) MIME-Version: 1.0 References: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-16-tabba@google.com> <498765f6-c20e-48f2-98e4-4134bfe150a3@redhat.com> In-Reply-To: <498765f6-c20e-48f2-98e4-4134bfe150a3@redhat.com> From: Fuad Tabba Date: Wed, 21 May 2025 09:24:56 +0100 X-Gm-Features: AX0GCFsFoNB1ieKR8Mpy2mR32AeGSlXaGdfHcg37_uYu8TA3HACi0fD0QWeAtgU Message-ID: Subject: Re: [PATCH v9 15/17] KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM To: Gavin Shan Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: wb8poeeiy3f1ebpzoi9ofiym9dz4jfen X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B8722180007 X-HE-Tag: 1747815934-307575 X-HE-Meta: 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 geSzLWCh kTnIklBVekz2BffjNszvU425zgPJQqbrhB6Kl5yFW7Os9bRPZQGsDYtdWVM7u13eLRqq636AlgovnMG4qUmCmZcILw/CQIKE/Slok7Ib+BuHNqkTFOT2FkmdJ+Dxur+aSDuQLyYxHXE7rT0T4g4//K04LDgVo/VtgyqempjF51zJ+RAb06OrtxYH2NHxhPncJxDTSbr4woQz+pxoh27oxBXxR0FF7NUxxVVtaVpSWZN5aeI3CP0Ujh2rja3WCOLzZLYPq8ZTnrlWHwcu7Fd6+KFlcCs70pzDMmmxbuUa+069cFhwH1ZH/hIoR9PBfyHViKRSwKcZKBu3fPFuDE5dmpnQjB3nrGMWtJxi3PJxU8paBINs= 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 Wed, 21 May 2025 at 03:47, Gavin Shan wrote: > > Hi Fuad, > > On 5/14/25 2:34 AM, Fuad Tabba wrote: > > This patch introduces the KVM capability KVM_CAP_GMEM_SHARED_MEM, which > > indicates that guest_memfd supports shared memory (when enabled by the > > flag). This support is limited to certain VM types, determined per > > architecture. > > > > This patch also updates the KVM documentation with details on the new > > capability, flag, and other information about support for shared memory > > in guest_memfd. > > > > Signed-off-by: Fuad Tabba > > --- > > Documentation/virt/kvm/api.rst | 18 ++++++++++++++++++ > > include/uapi/linux/kvm.h | 1 + > > virt/kvm/kvm_main.c | 4 ++++ > > 3 files changed, 23 insertions(+) > > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > > index 47c7c3f92314..86f74ce7f12a 100644 > > --- a/Documentation/virt/kvm/api.rst > > +++ b/Documentation/virt/kvm/api.rst > > @@ -6390,6 +6390,24 @@ most one mapping per page, i.e. binding multiple memory regions to a single > > guest_memfd range is not allowed (any number of memory regions can be bound to > > a single guest_memfd file, but the bound ranges must not overlap). > > > > +When the capability KVM_CAP_GMEM_SHARED_MEM is supported, the 'flags' field > > +supports GUEST_MEMFD_FLAG_SUPPORT_SHARED. Setting this flag on guest_memfd > > +creation enables mmap() and faulting of guest_memfd memory to host userspace. > > + > > +When the KVM MMU performs a PFN lookup to service a guest fault and the backing > > +guest_memfd has the GUEST_MEMFD_FLAG_SUPPORT_SHARED set, then the fault will > > +always be consumed from guest_memfd, regardless of whether it is a shared or a > > +private fault. > > + > > +For these memslots, userspace_addr is checked to be the mmap()-ed view of the > > +same range specified using gmem.pgoff. Other accesses by KVM, e.g., instruction > > +emulation, go via slot->userspace_addr. The slot->userspace_addr field can be > > +set to 0 to skip this check, which indicates that KVM would not access memory > > +belonging to the slot via its userspace_addr. > > + > > This paragraph needs to be removed if PATCH[08/17] is going to be dropped. Done. Thanks, /fuad > > [PATCH v9 08/17] KVM: guest_memfd: Check that userspace_addr and fd+offset refer to same range > > > +The use of GUEST_MEMFD_FLAG_SUPPORT_SHARED will not be allowed for CoCo VMs. > > +This is validated when the guest_memfd instance is bound to the VM. > > + > > See KVM_SET_USER_MEMORY_REGION2 for additional details. > > > > [...] > > Thanks, > Gavin >