Rework the not-yet-released KVM_CAP_GUEST_MEMFD_MMAP into a more generic KVM_CAP_GUEST_MEMFD_FLAGS capability so that adding new flags doesn't require a new capability, and so that developers aren't tempted to bundle multiple flags into a single capability. Note, kvm_vm_ioctl_check_extension_generic() can only return a 32-bit value, but that limitation can be easily circumvented by adding e.g. KVM_CAP_GUEST_MEMFD_FLAGS2 in the unlikely event guest_memfd supports more than 32 flags. Signed-off-by: Sean Christopherson --- Documentation/virt/kvm/api.rst | 10 +++++++--- include/uapi/linux/kvm.h | 2 +- tools/testing/selftests/kvm/guest_memfd_test.c | 13 ++++++------- virt/kvm/kvm_main.c | 7 +++++-- 4 files changed, 19 insertions(+), 13 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 6ae24c5ca559..7ba92f2ced38 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6432,9 +6432,13 @@ 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_GUEST_MEMFD_MMAP is supported, the 'flags' field -supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation -enables mmap() and faulting of guest_memfd memory to host userspace. +The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be +specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags: + + ============================ ================================================ + GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd file + descriptor. + ============================ ================================================ When the KVM MMU performs a PFN lookup to service a guest fault and the backing guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 6efa98a57ec1..b1d52d0c56ec 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -962,7 +962,7 @@ struct kvm_enable_cap { #define KVM_CAP_ARM_EL2_E2H0 241 #define KVM_CAP_RISCV_MP_STATE_RESET 242 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243 -#define KVM_CAP_GUEST_MEMFD_MMAP 244 +#define KVM_CAP_GUEST_MEMFD_FLAGS 244 struct kvm_irq_routing_irqchip { __u32 irqchip; diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index b3ca6737f304..3e58bd496104 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -262,19 +262,17 @@ static void test_guest_memfd_flags(struct kvm_vm *vm, uint64_t valid_flags) static void test_guest_memfd(unsigned long vm_type) { - uint64_t flags = 0; struct kvm_vm *vm; size_t total_size; size_t page_size; + uint64_t flags; int fd; page_size = getpagesize(); total_size = page_size * 4; vm = vm_create_barebones_type(vm_type); - - if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP)) - flags |= GUEST_MEMFD_FLAG_MMAP; + flags = vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS); test_create_guest_memfd_multiple(vm); test_create_guest_memfd_invalid_sizes(vm, flags, page_size); @@ -328,13 +326,14 @@ static void test_guest_memfd_guest(void) size_t size; int fd, i; - if (!kvm_has_cap(KVM_CAP_GUEST_MEMFD_MMAP)) + if (!kvm_check_cap(KVM_CAP_GUEST_MEMFD_FLAGS)) return; vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code); - TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP), - "Default VM type should always support guest_memfd mmap()"); + TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) & GUEST_MEMFD_FLAG_MMAP, + "Default VM type should support MMAP, supported flags = 0x%x", + vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS)); size = vm->page_size; fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 226faeaa8e56..e3a268757621 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4928,8 +4928,11 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) #ifdef CONFIG_KVM_GUEST_MEMFD case KVM_CAP_GUEST_MEMFD: return 1; - case KVM_CAP_GUEST_MEMFD_MMAP: - return !kvm || kvm_arch_supports_gmem_mmap(kvm); + case KVM_CAP_GUEST_MEMFD_FLAGS: + if (!kvm || kvm_arch_supports_gmem_mmap(kvm)) + return GUEST_MEMFD_FLAG_MMAP; + + return 0; #endif default: break; -- 2.51.0.618.g983fd99d29-goog