util/mmap-alloc: Pass flags instead of separate bools to qemu_ram_mmap()

Let's pass flags instead of bools to prepare for passing other flags and
update the documentation of qemu_ram_mmap(). Introduce new QEMU_MAP_
flags that abstract the mmap() PROT_ and MAP_ flag handling and simplify
it.

We expose only flags that are currently supported by qemu_ram_mmap().
Maybe, we'll see qemu_mmap() in the future as well that can implement these
flags.

Note: We don't use MAP_ flags as some flags (e.g., MAP_SYNC) are only
defined for some systems and we want to always be able to identify
these flags reliably inside qemu_ram_mmap() -- for example, to properly
warn when some future flags are not available or effective on a system.
Also, this way we can simplify PROT_ handling as well.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com> for memory backend and machine core
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210510114328.21835-8-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 27 insertions, 7 deletions

diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index 456ff87df1..90d0eee705 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -7,18 +7,22 @@ size_t qemu_fd_getpagesize(int fd);
 size_t qemu_mempath_getpagesize(const char *mem_path);
 
 /**
- * qemu_ram_mmap: mmap the specified file or device.
+ * qemu_ram_mmap: mmap anonymous memory, the specified file or device.
+ *
+ * mmap() abstraction to map guest RAM, simplifying flag handling, taking
+ * care of alignment requirements and installing guard pages.
  *
  * Parameters:
  *  @fd: the file or the device to mmap
  *  @size: the number of bytes to be mmaped
  *  @align: if not zero, specify the alignment of the starting mapping address;
  *          otherwise, the alignment in use will be determined by QEMU.
- *  @readonly: true for a read-only mapping, false for read/write.
- *  @shared: map has RAM_SHARED flag.
- *  @is_pmem: map has RAM_PMEM flag.
+ *  @qemu_map_flags: QEMU_MAP_* flags
  *  @map_offset: map starts at offset of map_offset from the start of fd
  *
+ * Internally, MAP_PRIVATE, MAP_ANONYMOUS and MAP_SHARED_VALIDATE are set
+ * implicitly based on other parameters.
+ *
  * Return:
  *  On success, return a pointer to the mapped area.
  *  On failure, return MAP_FAILED.
@@ -26,9 +30,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
 void *qemu_ram_mmap(int fd,
                     size_t size,
                     size_t align,
-                    bool readonly,
-                    bool shared,
-                    bool is_pmem,
+                    uint32_t qemu_map_flags,
                     off_t map_offset);
 
 void qemu_ram_munmap(int fd, void *ptr, size_t size);
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 18a9e3fb4c..37a38c4af3 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -366,6 +366,24 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *align, bool shared);
 void qemu_vfree(void *ptr);
 void qemu_anon_ram_free(void *ptr, size_t size);
 
+/*
+ * Abstraction of PROT_ and MAP_ flags as passed to mmap(), for example,
+ * consumed by qemu_ram_mmap().
+ */
+
+/* Map PROT_READ instead of PROT_READ | PROT_WRITE. */
+#define QEMU_MAP_READONLY   (1 << 0)
+
+/* Use MAP_SHARED instead of MAP_PRIVATE. */
+#define QEMU_MAP_SHARED     (1 << 1)
+
+/*
+ * Use MAP_SYNC | MAP_SHARED_VALIDATE if supported. Ignored without
+ * QEMU_MAP_SHARED. If mapping fails, warn and fallback to !QEMU_MAP_SYNC.
+ */
+#define QEMU_MAP_SYNC       (1 << 2)
+
+
 #define QEMU_MADV_INVALID -1
 
 #if defined(CONFIG_MADVISE)