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AJvYcCX7j+LB2wPNPVdPl3k+EQlm2KP9sSHaeQqMvindh/6CYIxQp0BjqT6SiINI72qkjIkbz+pJ7lvbPwo=@vger.kernel.org X-Gm-Message-State: AOJu0YyjAJ5knfOfVHPo3FDq06P8gGyLt4e81240sb26Yu1kutITT2Sv IZnVyfyMEkrMlJclRqQrAZks7zYXuvDZpmxXsTx6Vvizi+NMK7xz83jK9wVKv2T3abtL1xBZuSu PQSgNU6pk60rGq1mvwmedNe2E1A== X-Google-Smtp-Source: AGHT+IEK36TdUsL0vlOCqmspe4caiObjbOIOsGdu4QEVuayy/5SWQrXbR3hmNgi0EJY8rePbH10nOdC3ZkaAHHoKBw== X-Received: from pjyj23.prod.google.com ([2002:a17:90a:e617:b0:339:ae3b:2bc7]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:9988:b0:334:b8bb:b11d with SMTP id adf61e73a8af0-33dead4c65cmr3868140637.31.1761324494100; Fri, 24 Oct 2025 09:48:14 -0700 (PDT) Date: Fri, 24 Oct 2025 09:48:12 -0700 In-Reply-To: <727482ec42baa50cb1488ad89d02e732defda3db.1760731772.git.ackerleytng@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <727482ec42baa50cb1488ad89d02e732defda3db.1760731772.git.ackerleytng@google.com> Message-ID: Subject: Re: [RFC PATCH v1 16/37] KVM: selftests: Add support for mmap() on guest_memfd in core library From: Ackerley Tng To: cgroups@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org Cc: akpm@linux-foundation.org, binbin.wu@linux.intel.com, bp@alien8.de, brauner@kernel.org, chao.p.peng@intel.com, chenhuacai@kernel.org, corbet@lwn.net, dave.hansen@intel.com, dave.hansen@linux.intel.com, david@redhat.com, dmatlack@google.com, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, haibo1.xu@intel.com, hannes@cmpxchg.org, hch@infradead.org, hpa@zytor.com, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maobibo@loongson.cn, mathieu.desnoyers@efficios.com, maz@kernel.org, mhiramat@kernel.org, mhocko@kernel.org, mic@digikod.net, michael.roth@amd.com, mingo@redhat.com, mlevitsk@redhat.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, peterx@redhat.com, pgonda@google.com, prsampat@amd.com, pvorel@suse.cz, qperret@google.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, rostedt@goodmis.org, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shakeel.butt@linux.dev, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, tglx@linutronix.de, thomas.lendacky@amd.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, wyihan@google.com, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Content-Type: text/plain; charset="UTF-8" Ackerley Tng writes: > From: Sean Christopherson > > Accept gmem_flags in vm_mem_add() to be able to create a guest_memfd within > vm_mem_add(). > > When vm_mem_add() is used to set up a guest_memfd for a memslot, set up the > provided (or created) gmem_fd as the fd for the user memory region. This > makes it available to be mmap()-ed from just like fds from other memory > sources. mmap() from guest_memfd using the provided gmem_flags and > gmem_offset. > > Add a kvm_slot_to_fd() helper to provide convenient access to the file > descriptor of a memslot. > > Update existing callers of vm_mem_add() to pass 0 for gmem_flags to > preserve existing behavior. > > Signed-off-by: Sean Christopherson > [For guest_memfds, mmap() using gmem_offset instead of 0 all the time.] > Signed-off-by: Ackerley Tng > --- > tools/testing/selftests/kvm/include/kvm_util.h | 7 ++++++- > tools/testing/selftests/kvm/lib/kvm_util.c | 18 ++++++++++-------- > .../kvm/x86/private_mem_conversions_test.c | 2 +- > 3 files changed, 17 insertions(+), 10 deletions(-) > > > [...snip...] > > @@ -1050,13 +1049,16 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, > } > > region->fd = -1; > - if (backing_src_is_shared(src_type)) > + if (flags & KVM_MEM_GUEST_MEMFD && gmem_flags & GUEST_MEMFD_FLAG_MMAP) > + region->fd = kvm_dup(gmem_fd); > + else if (backing_src_is_shared(src_type)) > region->fd = kvm_memfd_alloc(region->mmap_size, > src_type == VM_MEM_SRC_SHARED_HUGETLB); > Doing this makes it hard to test the legacy dual-backing case. It actually broke x86/private_mem_conversions_test for the legacy dual-backing case because there's no way to mmap or provide a userspace_address from the memory provider that is not guest_memfd, as determined by src_type. I didn't test the legacy dual-backing case before posting this RFC and probably should have. > - region->mmap_start = kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE, > - vm_mem_backing_src_alias(src_type)->flag, > - region->fd); > + mmap_offset = flags & KVM_MEM_GUEST_MEMFD ? gmem_offset : 0; > + region->mmap_start = __kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE, > + vm_mem_backing_src_alias(src_type)->flag, > + region->fd, mmap_offset); > > TEST_ASSERT(!is_backing_src_hugetlb(src_type) || > region->mmap_start == align_ptr_up(region->mmap_start, backing_src_pagesz), > @@ -1117,7 +1119,7 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, > uint64_t gpa, uint32_t slot, uint64_t npages, > uint32_t flags) > { > - vm_mem_add(vm, src_type, gpa, slot, npages, flags, -1, 0); > + vm_mem_add(vm, src_type, gpa, slot, npages, flags, -1, 0, 0); > } > > /* > diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c > index 1969f4ab9b280..41f6b38f04071 100644 > --- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c > +++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c > @@ -399,7 +399,7 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t > for (i = 0; i < nr_memslots; i++) > vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i, > BASE_DATA_SLOT + i, slot_size / vm->page_size, > - KVM_MEM_GUEST_MEMFD, memfd, slot_size * i); > + KVM_MEM_GUEST_MEMFD, memfd, slot_size * i, 0); > > for (i = 0; i < nr_vcpus; i++) { > uint64_t gpa = BASE_DATA_GPA + i * per_cpu_size; > -- > 2.51.0.858.gf9c4a03a3a-goog