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Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Jason Gunthorpe , Vlastimil Babka Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, Ackerley Tng X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1777418714; l=3828; i=ackerleytng@google.com; s=20260225; h=from:subject:message-id; bh=/d2k8NxefQGN/ufZ9LnHGnYMKu34ADHcjvHKBhIXD7M=; b=1ULjpSvvqj0ZTKtSpsiMXgqtnYm7Snt35jmtyNxH17oWl3wy/V4Zf+IcNqc9/2lh+FZYBo3Rq O2h2lMIWdAOD1Tm3Ek0K9e45/q64b7b1AAg3Q7GDSAgbTfaw74Lzcqm X-Developer-Key: i=ackerleytng@google.com; a=ed25519; pk=sAZDYXdm6Iz8FHitpHeFlCMXwabodTm7p8/3/8xUxuU= X-Endpoint-Received: by B4 Relay for ackerleytng@google.com/20260225 with auth_id=649 X-Original-From: Ackerley Tng Reply-To: ackerleytng@google.com X-Rspam-User: X-Rspamd-Queue-Id: 10DD720009 X-Rspamd-Server: rspam06 X-Stat-Signature: bbjdcp3xe6dtfdxuxiy9uaaphp164ozg X-HE-Tag: 1777418738-846806 X-HE-Meta: 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 QggL3f5c eoKhF/yZcB4HLkk8WMvmTXTXaX9vEF5cAWAb7DCw3Nz1wXeKey1rhOTr7Sexhls15d5tbSN+eDN59Qu212GyZ+gTMEhvFrKUA/h6ZX0F5iEGjGIhcfw8Qgyy22rc9XyT5Kgu8Jv0AdBl34llfbfmmmyETPczfxqMeFIGyr587JYbvV/ntW8xB3JYZSZxstycK2xCt8UR4Ge4L7RUi2W6Z8KUO6Xr52c4SAlD8KQwnCd359VWE8Qz5Y04Axcm6F1SQ+gyKrsyaYxkqZY/AkRR6QdF42M7BP0jHnAgZ/Apvm9urVgnzfzTTHKpjD4Sw1lQkKtixov2m/HOpxk0EsEWCtEwr3oqNedBpEsdVRQi8FlyZybi+/Ypk6AosAkSChSVXxiaSHk2jvy6N0GKPtFXrU5tjZgdO5kJjLVVl Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Ackerley Tng 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 vmsplice to increment the refcount of a specific page. The reference is kept on the page by not reading data out from vmsplice's destination pipe. It then attempts to convert a range of pages, including the page with elevated refcount, 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/x86/guest_memfd_conversions_test.c | 80 ++++++++++++++++++++++ 1 file changed, 80 insertions(+) diff --git a/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c b/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c index 21918b83d3792..13bbc361eaeda 100644 --- a/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c +++ b/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c @@ -408,6 +408,86 @@ GMEM_CONVERSION_TEST_INIT_SHARED(forked_accesses) kvm_munmap(test_state, sizeof(*test_state)); } +static int pin_pipe[2] = { -1, -1 }; + +static void pin_pages(void *vaddr, size_t size) +{ + struct iovec iov = { + .iov_base = vaddr, + .iov_len = size, + }; + + if (pin_pipe[1] < 0) + TEST_ASSERT_EQ(pipe(pin_pipe), 0); + + TEST_ASSERT_EQ(vmsplice(pin_pipe[1], &iov, 1, 0), size); +} + +static void unpin_pages(void) +{ + close(pin_pipe[1]); + pin_pipe[1] = -1; + close(pin_pipe[0]); + pin_pipe[0] = -1; +} + +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 = 0; + int ret; + + do { + ret = __gmem_set_private(t->gmem_fd, offset, + nr_pages * page_size, &error_offset, + KVM_SET_MEMORY_ATTRIBUTES2_PRESERVE); + } 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); +} + +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, + KVM_SET_MEMORY_ATTRIBUTES2_PRESERVE); + + 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)); -- 2.54.0.545.g6539524ca2-goog