From 80445fed73a7d1a87e8ce96f6cb7d505e437f845 Mon Sep 17 00:00:00 2001

From: Peter Xu <peterx@redhat.com>

Date: Wed, 1 Feb 2023 16:10:54 -0500

Subject: [PATCH 4/8] util/userfaultfd: Add uffd_open()

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RH-Author: Peter Xu <peterx@redhat.com>

RH-MergeRequest: 149: Support /dev/userfaultfd

RH-Bugzilla: 2158704

RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

RH-Acked-by: quintela1 <quintela@redhat.com>

RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

RH-Commit: [2/3] 4c81696314ab26db47c3415fa2c2501c6a572b5c (peterx/qemu-kvm)

Add a helper to create the uffd handle.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Reviewed-by: Juan Quintela <quintela@redhat.com>

Signed-off-by: Peter Xu <peterx@redhat.com>

Signed-off-by: Juan Quintela <quintela@redhat.com>

(cherry picked from commit d5890ea0722831eea76a0efd23a496b3e8815fe8)

Signed-off-by: Peter Xu <peterx@redhat.com>

---

 include/qemu/userfaultfd.h   | 12 ++++++++++++

 migration/postcopy-ram.c     | 11 +++++------

 tests/qtest/migration-test.c |  4 ++--

 util/userfaultfd.c           | 13 +++++++++++--

 4 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/include/qemu/userfaultfd.h b/include/qemu/userfaultfd.h

index 6b74f92792..d764496f0b 100644

--- a/include/qemu/userfaultfd.h

+++ b/include/qemu/userfaultfd.h

@@ -13,10 +13,20 @@

 #ifndef USERFAULTFD_H

 #define USERFAULTFD_H

+#ifdef CONFIG_LINUX

+

 #include "qemu/osdep.h"

 #include "exec/hwaddr.h"

 #include <linux/userfaultfd.h>

+/**

+ * uffd_open(): Open an userfaultfd handle for current context.

+ *

+ * @flags: The flags we want to pass in when creating the handle.

+ *

+ * Returns: the uffd handle if >=0, or <0 if error happens.

+ */

+int uffd_open(int flags);

 int uffd_query_features(uint64_t *features);

 int uffd_create_fd(uint64_t features, bool non_blocking);

 void uffd_close_fd(int uffd_fd);

@@ -32,4 +42,6 @@ int uffd_wakeup(int uffd_fd, void *addr, uint64_t length);

 int uffd_read_events(int uffd_fd, struct uffd_msg *msgs, int count);

 bool uffd_poll_events(int uffd_fd, int tmo);

+#endif /* CONFIG_LINUX */

+

 #endif /* USERFAULTFD_H */

diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c

index b9a37ef255..0c55df0e52 100644

--- a/migration/postcopy-ram.c

+++ b/migration/postcopy-ram.c

@@ -37,6 +37,7 @@

 #include "qemu-file.h"

 #include "yank_functions.h"

 #include "tls.h"

+#include "qemu/userfaultfd.h"

 /* Arbitrary limit on size of each discard command,

  * keeps them around ~200 bytes

@@ -226,11 +227,9 @@ static bool receive_ufd_features(uint64_t *features)

     int ufd;

     bool ret = true;

-    /* if we are here __NR_userfaultfd should exists */

-    ufd = syscall(__NR_userfaultfd, O_CLOEXEC);

+    ufd = uffd_open(O_CLOEXEC);

     if (ufd == -1) {

-        error_report("%s: syscall __NR_userfaultfd failed: %s", __func__,

-                     strerror(errno));

+        error_report("%s: uffd_open() failed: %s", __func__, strerror(errno));

         return false;

     }

@@ -375,7 +374,7 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)

         goto out;

     }

-    ufd = syscall(__NR_userfaultfd, O_CLOEXEC);

+    ufd = uffd_open(O_CLOEXEC);

     if (ufd == -1) {

         error_report("%s: userfaultfd not available: %s", __func__,

                      strerror(errno));

@@ -1160,7 +1159,7 @@ static int postcopy_temp_pages_setup(MigrationIncomingState *mis)

 int postcopy_ram_incoming_setup(MigrationIncomingState *mis)

 {

     /* Open the fd for the kernel to give us userfaults */

-    mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);

+    mis->userfault_fd = uffd_open(O_CLOEXEC | O_NONBLOCK);

     if (mis->userfault_fd == -1) {

         error_report("%s: Failed to open userfault fd: %s", __func__,

                      strerror(errno));

diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c

index dbde726adf..0100e1bdbc 100644

--- a/tests/qtest/migration-test.c

+++ b/tests/qtest/migration-test.c

@@ -61,14 +61,14 @@ static bool uffd_feature_thread_id;

 #if defined(__linux__) && defined(__NR_userfaultfd) && defined(CONFIG_EVENTFD)

 #include <sys/eventfd.h>

 #include <sys/ioctl.h>

-#include <linux/userfaultfd.h>

+#include "qemu/userfaultfd.h"

 static bool ufd_version_check(void)

 {

     struct uffdio_api api_struct;

     uint64_t ioctl_mask;

-    int ufd = syscall(__NR_userfaultfd, O_CLOEXEC);

+    int ufd = uffd_open(O_CLOEXEC);

     if (ufd == -1) {

         g_test_message("Skipping test: userfaultfd not available");

diff --git a/util/userfaultfd.c b/util/userfaultfd.c

index f1cd6af2b1..4953b3137d 100644

--- a/util/userfaultfd.c

+++ b/util/userfaultfd.c

@@ -19,6 +19,15 @@

 #include <sys/syscall.h>

 #include <sys/ioctl.h>

+int uffd_open(int flags)

+{

+#if defined(__NR_userfaultfd)

+    return syscall(__NR_userfaultfd, flags);

+#else

+    return -EINVAL;

+#endif

+}

+

 /**

  * uffd_query_features: query UFFD features

  *

@@ -32,7 +41,7 @@ int uffd_query_features(uint64_t *features)

     struct uffdio_api api_struct = { 0 };

     int ret = -1;

-    uffd_fd = syscall(__NR_userfaultfd, O_CLOEXEC);

+    uffd_fd = uffd_open(O_CLOEXEC);

     if (uffd_fd < 0) {

         trace_uffd_query_features_nosys(errno);

         return -1;

@@ -69,7 +78,7 @@ int uffd_create_fd(uint64_t features, bool non_blocking)

     uint64_t ioctl_mask = BIT(_UFFDIO_REGISTER) | BIT(_UFFDIO_UNREGISTER);

     flags = O_CLOEXEC | (non_blocking ? O_NONBLOCK : 0);

-    uffd_fd = syscall(__NR_userfaultfd, flags);

+    uffd_fd = uffd_open(flags);

     if (uffd_fd < 0) {

         trace_uffd_create_fd_nosys(errno);

         return -1;

-- 

2.31.1