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AJvYcCVQ+Duo7m7XbqV52f5S0Ys9v4IO/EGwXYY7kr2jJBsnGPccuuYj+TTAvf6lrglMk7RvCtkBypTxFA==@kvack.org X-Gm-Message-State: AOJu0YzTpb1KXrjZgHeZJXyx/QkFGRPKn62T9t6SMvgmR/3STvSZeFIq zHTAJkReJ1vCSIRIqBCKO5Ee2+B06C6eioKAK1oWnG3WAuHmY2hk7m/X0LSWgIHRXID10A5fuIJ +5LP/kFDsGqwQHF0iysEX126HOQ== X-Google-Smtp-Source: AGHT+IHVYfbeJHjmJQIxf3lnI6xML61YGFIRkStopZSXJJvTgLI8jTgXjo0mAYsj6xfs9PsRIMTiStrABfsfvN8xtQ== X-Received: from pjbqx13.prod.google.com ([2002:a17:90b:3e4d:b0:32d:e4c6:7410]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:28c5:b0:33b:c5c7:511a with SMTP id 98e67ed59e1d1-33bc5c75327mr6623268a91.15.1760731993183; Fri, 17 Oct 2025 13:13:13 -0700 (PDT) Date: Fri, 17 Oct 2025 13:12:08 -0700 In-Reply-To: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.51.0.858.gf9c4a03a3a-goog Message-ID: Subject: [RFC PATCH v1 27/37] KVM: selftests: guest_memfd: Test conversion with elevated page refcount 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: ackerleytng@google.com, 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" X-Rspamd-Server: rspam05 X-Stat-Signature: ycsmsa78o6fot1og6xxqzfzefkfiempp X-Rspam-User: X-Rspamd-Queue-Id: C35E2120009 X-HE-Tag: 1760731994-670198 X-HE-Meta: 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 IX6kj6Hg 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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: Add a selftest to verify that converting a shared guest_memfd page to a private page fails if the page has an elevated reference count. When KVM converts a shared page to a private one, it expects the page to have a reference count equal to the reference counts taken by the filemap. If another kernel subsystem holds a reference to the page, for example via pin_user_pages(), the conversion must be aborted. This test uses the gup_test debugfs interface (which requires CONFIG_GUP_TEST) to call pin_user_pages() on a specific page, artificially increasing its reference count. It then attempts to convert a range of pages, including the pinned page, from shared to private. The test asserts that both bulk and single-page conversion attempts correctly fail with EAGAIN for the pinned page. After the page is unpinned, the test verifies that subsequent conversions succeed. Signed-off-by: Ackerley Tng Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson --- .../kvm/guest_memfd_conversions_test.c | 82 +++++++++++++++++++ 1 file changed, 82 insertions(+) diff --git a/tools/testing/selftests/kvm/guest_memfd_conversions_test.c b/tools/testing/selftests/kvm/guest_memfd_conversions_test.c index e6abf2d30c62d..856166f1b1dfc 100644 --- a/tools/testing/selftests/kvm/guest_memfd_conversions_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_conversions_test.c @@ -14,6 +14,7 @@ #include "kselftest_harness.h" #include "test_util.h" #include "ucall_common.h" +#include "../../../../mm/gup_test.h" FIXTURE(gmem_conversions) { struct kvm_vcpu *vcpu; @@ -404,6 +405,87 @@ GMEM_CONVERSION_TEST_INIT_SHARED(forked_accesses) kvm_munmap(test_state, sizeof(*test_state)); } +static int gup_test_fd; + +static void pin_pages(void *vaddr, uint64_t size) +{ + const struct pin_longterm_test args = { + .addr = (uint64_t)vaddr, + .size = size, + .flags = PIN_LONGTERM_TEST_FLAG_USE_WRITE, + }; + + gup_test_fd = open("/sys/kernel/debug/gup_test", O_RDWR); + TEST_REQUIRE(gup_test_fd >= 0); + + TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_START, &args), 0); +} + +static void unpin_pages(void) +{ + if (gup_test_fd > 0) + TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_STOP), 0); +} + +static void test_convert_to_private_fails(test_data_t *t, loff_t pgoff, + size_t nr_pages, + loff_t expected_error_offset) +{ + loff_t offset = pgoff * page_size; + loff_t error_offset = -1ul; + int ret; + + do { + ret = __gmem_set_private(t->gmem_fd, offset, + nr_pages * page_size, &error_offset); + } while (ret == -1 && errno == EINTR); + TEST_ASSERT(ret == -1 && errno == EAGAIN, + "Wanted EAGAIN on page %lu, got %d (ret = %d)", pgoff, + errno, ret); + TEST_ASSERT_EQ(error_offset, expected_error_offset); +} + +/* + * This test depends on CONFIG_GUP_TEST to provide a kernel module that exposes + * pin_user_pages() to userspace. + */ +GMEM_CONVERSION_MULTIPAGE_TEST_INIT_SHARED(elevated_refcount, 4) +{ + int i; + + pin_pages(t->mem + test_page * page_size, page_size); + + for (i = 0; i < nr_pages; i++) + test_shared(t, i, 0, 'A', 'B'); + + /* + * Converting in bulk should fail as long any page in the range has + * unexpected refcounts. + */ + test_convert_to_private_fails(t, 0, nr_pages, test_page * page_size); + + for (i = 0; i < nr_pages; i++) { + /* + * Converting page-wise should also fail as long any page in the + * range has unexpected refcounts. + */ + if (i == test_page) + test_convert_to_private_fails(t, i, 1, test_page * page_size); + else + test_convert_to_private(t, i, 'B', 'C'); + } + + unpin_pages(); + + gmem_set_private(t->gmem_fd, 0, nr_pages * page_size); + + for (i = 0; i < nr_pages; i++) { + char expected = i == test_page ? 'B' : 'C'; + + test_private(t, i, expected, 'D'); + } +} + int main(int argc, char *argv[]) { TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM)); -- 2.51.0.858.gf9c4a03a3a-goog