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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=1778185365; l=3740; i=ackerleytng@google.com; s=20260225; h=from:subject:message-id; bh=ShebxFNR8cyYKJhqdsAuEPs4lv0Wp74neBFpE5OoHfk=; b=oGY6oGbsKFd03bkt91zRl6V9nz0Z0kJq6BalAUuo0PhX7ynYcZMAdcRPTk00X1HA2FWG22is5 Tb8i91J3ExLCt/zmSi/FFUcbyFlEyOIi8Y2aDRbzCTeE+/A3r3m3/hZ 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-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A90594000D X-Stat-Signature: rwjatd8w7naqkxyrxycgmkef57qsmhhw X-Rspam-User: X-HE-Tag: 1778185386-569455 X-HE-Meta: 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 eZASCn/G 5FLXf0/xOiqVukhPdp9/BLXdr4G4M0sZ2krMsI+ihUuRkKyAdunQ1YRjODbb0gSw49GSYcL2orLbVo3wp3lRohz16YEpAfHwYQhVga7nJM1FC9ISc0V8aJul2TIj/w4XX4e2w2SuPIqBEksuSaB7ym98KYuAf72L7c04r8gOuVTiWDgZJYqWuatF3MN5RW879glmIW98/78EgDTE5tWbZ5ypiAwu1DkxYzbPdjiGc1f4TwdVFcyqX5gvDz8rVYWkThkxs57xlB913ueVtZgIILtqlFPKhdzRLWl5LIrSrB8TTIUFjhl2k8SAeTutmc2/BQlVxuM6+x5+7jPUUq1sDJo7gT8AaiosUjL1GfQTCTZ8mYfo0gxgSoEsmNpRDRMiJQy8PaGDs9DqPJEqwIvd6fssXrwcGSHulsXNJ 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 | 78 ++++++++++++++++++++++ 1 file changed, 78 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 4c33e21f04972..00a200a3019ef 100644 --- a/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c +++ b/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c @@ -397,6 +397,84 @@ 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); + } 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); + + 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)); -- 2.54.0.563.g4f69b47b94-goog