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[2003:d8:2f25:9c00:e2c7:6eb5:8a51:1c60]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca888afsm19250604f8f.64.2025.05.21.01.06.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 01:06:32 -0700 (PDT) Message-ID: <338c5df3-c7c7-4b44-8e09-09ee77563ff2@redhat.com> Date: Wed, 21 May 2025 10:06:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 15/17] KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: 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, 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 References: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-16-tabba@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: AAB6A100011 X-Stat-Signature: r979n368k7az3aaxdj791h195za9e39n X-Rspam-User: X-HE-Tag: 1747814796-659268 X-HE-Meta: U2FsdGVkX18d7mILJscGKCUs7v/trVOGfSkLNMoUR+bZbTi9UMoGYbVaT4UVlDMMXapf0bmuKztYVOnd8zzdLhH2eqh2rfEh34F6bCCk6deiy9h01G3Za/gCM0cP2wvd0QJ8DxJoOVIh7mGTD+cPZZ1PcZrMU7QxG47rvjz2MMBOjAJPXPWWCoNntHia+bC7KLjopQIWLWZ0JaikSetwptOgxptN6P7UHqIGRlhR9UfchNxxLQMiRXqsWnOZn2XytcJC77DA8FJ9yNT2slfuU9dyJWMx4DNnWj5o4uxbRqe/zBvCNPVPwYctBPAujZQrXVvMzjpMDZBaQNcGZnlprneBJf93Ch1hNRDteSlI8muljkann45halJK1sw9b0EQm4znK0pWcDL/ODcQFBlHQ2savJ2B6rKue42LxD1t/ork2BoQjmpXkmKJ12FGWxRwtCXtPxOjaDhT+9KiJmqkNCQUSBPsMLbSn7RLiAtNE7w/wDV6ZMazjCLngXcXSoNzQHKtI7uWJpjr0D3mDjAz5jlDz5bYa9vvRv2EcTeq3PZwV16xLTSOq1RgydTPr5AoeVh/x47+ahlq2SYRAD9zC7ubwcIbNyKhfd2S8W5O1F/7wGoRFYHR0jTpWXHUcNKJNYyEDgC/505GbTX734TB0yTahIrfG0ogEkkvUe+7vNMeR8+eHDqMq9+nY5c43fA7mwW3OUL+0CDS0Qb6YVO6KQ7yDzmAuAcpb3FSHVB3jTIJeDuw60SO7jPjmnSiYJtbqkXadL8kl+3wYbY/QuU05fSviQdLCb5yWZUuGW8w2/q17MOwGZKNO7oD797zR+ZpWVzUxXuFu/YNpy8ZJwbJE2RVsFMOJYRGEMSjuuj0HVLpHSF9SosYI+OFDQ6MACSBx69JkTalEq7eCM2FD5wwjT774AF0nX254B9uOsr4dN0/8mdxQet7vy5wU53dH1mqk52EA3s6Us20/WsJm2w LwGJf3PZ 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 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 13.05.25 18:34, 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. > + > +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. With Gavin's comment addressed Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb