From 13a59d404bb3edaed9e42c94432be28fb9a65c26 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Fri, 5 Mar 2021 17:20:37 +0100
Subject: [PATCH] util/mmap-alloc: Pass MAP_ flags instead of separate bools to
qemu_ram_mmap()
Let's pass MAP_ flags instead of bools to prepare for passing other MAP_
flags and update the documentation of qemu_ram_mmap(). Only allow selected
MAP_ flags (MAP_SHARED, MAP_SYNC) to be passed and keep setting other
flags implicitly.
Keep the "readonly" flag, as it cannot be expressed via MAP_ flags.
Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/qemu/mmap-alloc.h | 19 ++++++++++++++-----
softmmu/physmem.c | 6 ++++--
util/mmap-alloc.c | 13 ++++++++-----
util/oslib-posix.c | 3 ++-
4 files changed, 28 insertions(+), 13 deletions(-)
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index 456ff87df1..27ef374810 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -7,7 +7,10 @@ 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.
+ *
+ * QEMU's 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
@@ -15,10 +18,17 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
* @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.
+ * @map_flags: supported MAP_* flags: MAP_SHARED, MAP_SYNC
* @map_offset: map starts at offset of map_offset from the start of fd
*
+ * Implicitly handled map_flags:
+ * - MAP PRIVATE: With !MAP_SHARED
+ * - MAP_ANONYMOUS: With fd < 0
+ * - MAP_SHARED_VALIDATE: With MAP_SYNC && MAP_SHARED
+ *
+ * MAP_SYNC is ignored without MAP_SHARED. If mapping via MAP_SYNC fails,
+ * warn and fallback to mapping without MAP_SYNC.
+ *
* Return:
* On success, return a pointer to the mapped area.
* On failure, return MAP_FAILED.
@@ -27,8 +37,7 @@ void *qemu_ram_mmap(int fd,
size_t size,
size_t align,
bool readonly,
- bool shared,
- bool is_pmem,
+ uint32_t map_flags,
off_t map_offset);
void qemu_ram_munmap(int fd, void *ptr, size_t size);
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 8f3d286e12..1336884b51 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1533,6 +1533,7 @@ static void *file_ram_alloc(RAMBlock *block,
off_t offset,
Error **errp)
{
+ uint32_t map_flags;
void *area;
block->page_size = qemu_fd_getpagesize(fd);
@@ -1580,9 +1581,10 @@ static void *file_ram_alloc(RAMBlock *block,
perror("ftruncate");
}
+ map_flags = (block->flags & RAM_SHARED) ? MAP_SHARED : 0;
+ map_flags |= (block->flags & RAM_PMEM) ? MAP_SYNC : 0;
area = qemu_ram_mmap(fd, memory, block->mr->align, readonly,
- block->flags & RAM_SHARED, block->flags & RAM_PMEM,
- offset);
+ map_flags, offset);
if (area == MAP_FAILED) {
error_setg_errno(errp, errno,
"unable to map backing store for guest RAM");
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 0e2bd7bc0e..b558f1675a 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -119,16 +119,20 @@ static void *mmap_reserve(size_t size, int fd)
* it accessible.
*/
static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly,
- bool shared, bool is_pmem, off_t map_offset)
+ uint32_t map_flags, off_t map_offset)
{
+ const bool shared = map_flags & MAP_SHARED;
+ const bool sync = map_flags & MAP_SYNC;
const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
int map_sync_flags = 0;
int flags = MAP_FIXED;
void *activated_ptr;
+ g_assert(!(map_flags & ~(MAP_SHARED | MAP_SYNC)));
+
flags |= fd == -1 ? MAP_ANONYMOUS : 0;
flags |= shared ? MAP_SHARED : MAP_PRIVATE;
- if (shared && is_pmem) {
+ if (shared && sync) {
map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
}
@@ -174,8 +178,7 @@ void *qemu_ram_mmap(int fd,
size_t size,
size_t align,
bool readonly,
- bool shared,
- bool is_pmem,
+ uint32_t map_flags,
off_t map_offset)
{
const size_t guard_pagesize = mmap_guard_pagesize(fd);
@@ -199,7 +202,7 @@ void *qemu_ram_mmap(int fd,
offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
- ptr = mmap_activate(guardptr + offset, size, fd, readonly, shared, is_pmem,
+ ptr = mmap_activate(guardptr + offset, size, fd, readonly, map_flags,
map_offset);
if (ptr == MAP_FAILED) {
munmap(guardptr, total);
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 36820fec16..95e2b85279 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -229,8 +229,9 @@ void *qemu_memalign(size_t alignment, size_t size)
/* alloc shared memory pages */
void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
{
+ const uint32_t map_flags = shared ? MAP_SHARED : 0;
size_t align = QEMU_VMALLOC_ALIGN;
- void *ptr = qemu_ram_mmap(-1, size, align, false, shared, false, 0);
+ void *ptr = qemu_ram_mmap(-1, size, align, false, map_flags, 0);
if (ptr == MAP_FAILED) {
return NULL;