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AJvYcCVSYlTxZVsolCTNDaYhyEvtaQr+VesZ8GUZoJHmtTZuQKVlEY8JSb7Eu8sqe9/0sVVmqBzhgtPgACQ=@vger.kernel.org X-Gm-Message-State: AOJu0YyTL/bJV+u1S3fylpwYdAriuqusKOQhROT1OlHDg104BfwOS7W0 xtAw4qpoS69eqbmBp46sYEwat2BpLesYxJl2Ao4+SsSljM+7zVfdjjhtubb9G63lyo9Zd3Eaw2U 5VgPlxo/X+oluGw== X-Google-Smtp-Source: AGHT+IFXk6DKJ2LvWY2ZBOreY5EWyiD1FLIIWcEezkT9L8CiZAonL3OXc94rN18lwM8G/At6waViWG4yx0JY7g== X-Received: from wmbka6.prod.google.com ([2002:a05:600c:5846:b0:470:ffaa:ae5e]) (user=jackmanb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:3b8b:b0:471:989:9d7b with SMTP id 5b1f17b1804b1-4773086d53amr4625785e9.21.1761844712453; Thu, 30 Oct 2025 10:18:32 -0700 (PDT) Date: Thu, 30 Oct 2025 17:18:31 +0000 In-Reply-To: <20250924152214.7292-9-roypat@amazon.co.uk> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250924151101.2225820-4-patrick.roy@campus.lmu.de> <20250924152214.7292-1-roypat@amazon.co.uk> <20250924152214.7292-9-roypat@amazon.co.uk> X-Mailer: aerc 0.21.0 Message-ID: Subject: Re: [PATCH v7 12/12] KVM: selftests: Test guest execution from direct map removed gmem From: Brendan Jackman To: "Roy, Patrick" Cc: "pbonzini@redhat.com" , "corbet@lwn.net" , "maz@kernel.org" , "oliver.upton@linux.dev" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "luto@kernel.org" , "peterz@infradead.org" , "willy@infradead.org" , "akpm@linux-foundation.org" , "david@redhat.com" , "lorenzo.stoakes@oracle.com" , "Liam.Howlett@oracle.com" , "vbabka@suse.cz" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "song@kernel.org" , "jolsa@kernel.org" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "shuah@kernel.org" , "seanjc@google.com" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "Cali, Marco" , "Kalyazin, Nikita" , "Thomson, Jack" , "derekmn@amazon.co.uk" , "tabba@google.com" , "ackerleytng@google.com" Content-Type: text/plain; charset="UTF-8" On Wed Sep 24, 2025 at 3:22 PM UTC, Patrick Roy wrote: > Add a selftest that loads itself into guest_memfd (via > GUEST_MEMFD_FLAG_MMAP) and triggers an MMIO exit when executed. This > exercises x86 MMIO emulation code inside KVM for guest_memfd-backed > memslots where the guest_memfd folios are direct map removed. > Particularly, it validates that x86 MMIO emulation code (guest page > table walks + instruction fetch) correctly accesses gmem through the VMA > that's been reflected into the memslot's userspace_addr field (instead > of trying to do direct map accesses). > > Signed-off-by: Patrick Roy > --- > .../selftests/kvm/set_memory_region_test.c | 50 +++++++++++++++++-- > 1 file changed, 46 insertions(+), 4 deletions(-) > > diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c > index ce3ac0fd6dfb..cb3bc642d376 100644 > --- a/tools/testing/selftests/kvm/set_memory_region_test.c > +++ b/tools/testing/selftests/kvm/set_memory_region_test.c > @@ -603,6 +603,41 @@ static void test_mmio_during_vectoring(void) > > kvm_vm_free(vm); > } > + > +static void guest_code_trigger_mmio(void) > +{ > + /* > + * Read some GPA that is not backed by a memslot. KVM consider this > + * as MMIO and tell userspace to emulate the read. > + */ > + READ_ONCE(*((uint64_t *)MEM_REGION_GPA)); > + > + GUEST_DONE(); > +} > + > +static void test_guest_memfd_mmio(void) > +{ > + struct kvm_vm *vm; > + struct kvm_vcpu *vcpu; > + struct vm_shape shape = { > + .mode = VM_MODE_DEFAULT, > + .src_type = VM_MEM_SRC_GUEST_MEMFD_NO_DIRECT_MAP, > + }; > + pthread_t vcpu_thread; > + > + pr_info("Testing MMIO emulation for instructions in gmem\n"); > + > + vm = __vm_create_shape_with_one_vcpu(shape, &vcpu, 0, guest_code_trigger_mmio); When I run this test on my minimal config in a nested VM I get: [root@testvm:~]# /nix/store/xlxd60n7v1qfr6s5zxda410zrzdd0xc2-kselftests/bin/run_kselftest.sh -t kvm:set_memory_region_test TAP version 13 1..1 # timeout set to 120 # selftests: kvm: set_memory_region_test # Random seed: 0x6b8b4567 # Testing KVM_RUN with zero added memory regions # Testing MMIO during vectoring error handling # Allowed number of memory slots: 32764 # Adding slots 0..32763, each memory region with 2048K size # Testing MMIO emulation for instructions in gmem # ==== Test Assertion Failure ==== # lib/kvm_util.c:1118: region->mmap_start != MAP_FAILED # pid=614 tid=614 errno=19 - No such device # 1 0x0000000000407b02: vm_mem_add at ??:? # 2 0x000000000040a924: __vm_create at ??:? # 3 0x000000000040ab16: __vm_create_shape_with_one_vcpu at ??:? # 4 0x00000000004042cf: main at ??:? # 5 0x00007faa6b08a47d: ?? ??:0 # 6 0x00007faa6b08a538: ?? ??:0 # 7 0x0000000000404384: _start at ??:? # mmap() failed, rc: -1 errno: 19 (No such device) Here's the kconfig I'm using (basically defconfig+KVM): https://gist.githubusercontent.com/bjackman/4ea941ef5072606769211f3b000c8ed7/raw/73808882ddae6ff2ae8a0be85ac977b2980f7292/kconfig.txt Sorry I'm too ignorant about KVM to know what I'm missing here but I guess it's a missing TEST_REQUIRE()?