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Re: [Qemu-devel] [PATCH v2] hostmem-file: reject invalid pmem file sizes
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH v2] hostmem-file: reject invalid pmem file sizes |
Date: |
Wed, 13 Feb 2019 13:36:44 +0100 |
On Wed, 13 Feb 2019 16:53:54 +0800
Wei Yang <address@hidden> wrote:
> On Wed, Feb 13, 2019 at 03:14:01PM +0800, Stefan Hajnoczi wrote:
> >Guests started with NVDIMMs larger than the underlying host file produce
> >confusing errors inside the guest. This happens because the guest
> >accesses pages beyond the end of the file.
> >
> >Check the pmem file size on startup and print a clear error message if
> >the size is invalid.
> >
> >Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1669053
> >Cc: Haozhong Zhang <address@hidden>
> >Cc: Zhang Yi <address@hidden>
> >Cc: Eduardo Habkost <address@hidden>
> >Cc: Igor Mammedov <address@hidden>
> >Signed-off-by: Stefan Hajnoczi <address@hidden>
> >---
> >v2:
> > * Propagate qemu_get_pmem_size() errors [Igor]
> >
> > include/qemu/osdep.h | 13 ++++++++++
> > backends/hostmem-file.c | 22 +++++++++++++++++
> > util/oslib-posix.c | 53 +++++++++++++++++++++++++++++++++++++++++
> > util/oslib-win32.c | 5 ++++
> > 4 files changed, 93 insertions(+)
> >
> >diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> >index 840af09cb0..303d315c5d 100644
> >--- a/include/qemu/osdep.h
> >+++ b/include/qemu/osdep.h
> >@@ -570,6 +570,19 @@ void qemu_set_tty_echo(int fd, bool echo);
> > void os_mem_prealloc(int fd, char *area, size_t sz, int smp_cpus,
> > Error **errp);
> >
> >+/**
> >+ * qemu_get_pmem_size:
> >+ * @filename: path to a pmem file
> >+ * @errp: pointer to a NULL-initialized error object
> >+ *
> >+ * Determine the size of a persistent memory file. Besides supporting
> >files on
> >+ * DAX file systems, this function also supports Linux devdax character
> >+ * devices.
> >+ *
> >+ * Returns: the size or 0 on failure
> >+ */
> >+uint64_t qemu_get_pmem_size(const char *filename, Error **errp);
> >+
> > /**
> > * qemu_get_pid_name:
> > * @pid: pid of a process
> >diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> >index ba601ce940..d62689179b 100644
> >--- a/backends/hostmem-file.c
> >+++ b/backends/hostmem-file.c
> >@@ -46,6 +46,28 @@ file_backend_memory_alloc(HostMemoryBackend *backend,
> >Error **errp)
> > gchar *name;
> > #endif
> >
> >+ /*
> >+ * Verify pmem file size since starting a guest with an incorrect size
> >+ * leads to confusing failures inside the guest.
> >+ */
> >+ if (fb->is_pmem && fb->mem_path) {
> >+ Error *local_err = NULL;
> >+ uint64_t size;
> >+
> >+ size = qemu_get_pmem_size(fb->mem_path, &local_err);
> >+ if (!size) {
> >+ error_propagate(errp, local_err);
> >+ return;
> >+ }
> >+
> >+ if (backend->size > size) {
> >+ error_setg(errp, "size property %" PRIu64 " is larger than "
> >+ "pmem file \"%s\" size %" PRIu64, backend->size,
> >+ fb->mem_path, size);
> >+ return;
> >+ }
> >+ }
> >+
>
> -mem-path is only supported on POSIX host.
>
> So how about put this in the last code block before doing the real memory
> region init?
Indeed, evaluating file would be better done only if we didn't fail
size/mempath checks first.
> BTW, I suggest to cleanup file_backend_memory_alloc() to make POSIX/non-POSIX
> situation clear to understand.
that's a separate patch, I'll reply with it here so Sefan could pick it (due to
conflicts the change would create)
>
> > if (!backend->size) {
> > error_setg(errp, "can't create backend with size 0");
> > return;
> >diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> >index 37c5854b9c..10d90d1783 100644
> >--- a/util/oslib-posix.c
> >+++ b/util/oslib-posix.c
> >@@ -500,6 +500,59 @@ void os_mem_prealloc(int fd, char *area, size_t memory,
> >int smp_cpus,
> > }
> > }
> >
> >+uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> >+{
> >+ struct stat st;
> >+
> >+ if (stat(filename, &st) < 0) {
> >+ error_setg(errp, "unable to stat pmem file \"%s\"", filename);
> >+ return 0;
> >+ }
> >+
> >+#if defined(__linux__)
> >+ /* Special handling for devdax character devices */
> >+ if (S_ISCHR(st.st_mode)) {
> >+ char *subsystem_path = NULL;
> >+ char *subsystem = NULL;
> >+ char *size_path = NULL;
> >+ char *size_str = NULL;
> >+ uint64_t ret = 0;
> >+
> >+ subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
> >+ major(st.st_rdev),
> >minor(st.st_rdev));
> >+ subsystem = g_file_read_link(subsystem_path, NULL);
> >+ if (!subsystem) {
> >+ error_setg(errp, "unable to read subsystem for pmem file
> >\"%s\"",
> >+ filename);
> >+ goto devdax_err;
> >+ }
> >+
> >+ if (!g_str_has_suffix(subsystem, "/dax")) {
> >+ error_setg(errp, "pmem file \"%s\" is not a dax device",
> >filename);
> >+ goto devdax_err;
> >+ }
> >+
> >+ size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",
> >+ major(st.st_rdev), minor(st.st_rdev));
> >+ if (!g_file_get_contents(size_path, &size_str, NULL, NULL)) {
> >+ error_setg(errp, "unable to read size for pmem file \"%s\"",
> >+ size_path);
> >+ goto devdax_err;
> >+ }
> >+
> >+ ret = g_ascii_strtoull(size_str, NULL, 0);
> >+
> >+devdax_err:
> >+ g_free(size_str);
> >+ g_free(size_path);
> >+ g_free(subsystem);
> >+ g_free(subsystem_path);
> >+ return ret;
> >+ }
> >+#endif /* defined(__linux__) */
> >+
> >+ return st.st_size;
> >+}
> >
> > char *qemu_get_pid_name(pid_t pid)
> > {
> >diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> >index b4c17f5dfa..bd633afab6 100644
> >--- a/util/oslib-win32.c
> >+++ b/util/oslib-win32.c
> >@@ -560,6 +560,11 @@ void os_mem_prealloc(int fd, char *area, size_t memory,
> >int smp_cpus,
> > }
> > }
> >
> >+uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> >+{
> >+ error_setg(errp, "pmem support not available");
> >+ return 0;
> >+}
> >
> > char *qemu_get_pid_name(pid_t pid)
> > {
> >--
> >2.20.1
> >
>