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>
This commit is contained in:
David Hildenbrand 2021-05-10 13:43:20 +02:00 committed by Paolo Bonzini
parent ebef62d0e5
commit b444f5c079
5 changed files with 42 additions and 18 deletions

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@ -7,18 +7,22 @@ size_t qemu_fd_getpagesize(int fd);
size_t qemu_mempath_getpagesize(const char *mem_path); 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: * Parameters:
* @fd: the file or the device to mmap * @fd: the file or the device to mmap
* @size: the number of bytes to be mmaped * @size: the number of bytes to be mmaped
* @align: if not zero, specify the alignment of the starting mapping address; * @align: if not zero, specify the alignment of the starting mapping address;
* otherwise, the alignment in use will be determined by QEMU. * otherwise, the alignment in use will be determined by QEMU.
* @readonly: true for a read-only mapping, false for read/write. * @qemu_map_flags: QEMU_MAP_* flags
* @shared: map has RAM_SHARED flag.
* @is_pmem: map has RAM_PMEM flag.
* @map_offset: map starts at offset of map_offset from the start of fd * @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: * Return:
* On success, return a pointer to the mapped area. * On success, return a pointer to the mapped area.
* On failure, return MAP_FAILED. * On failure, return MAP_FAILED.
@ -26,9 +30,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
void *qemu_ram_mmap(int fd, void *qemu_ram_mmap(int fd,
size_t size, size_t size,
size_t align, size_t align,
bool readonly, uint32_t qemu_map_flags,
bool shared,
bool is_pmem,
off_t map_offset); off_t map_offset);
void qemu_ram_munmap(int fd, void *ptr, size_t size); void qemu_ram_munmap(int fd, void *ptr, size_t size);

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@ -366,6 +366,24 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *align, bool shared);
void qemu_vfree(void *ptr); void qemu_vfree(void *ptr);
void qemu_anon_ram_free(void *ptr, size_t size); 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 #define QEMU_MADV_INVALID -1
#if defined(CONFIG_MADVISE) #if defined(CONFIG_MADVISE)

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@ -1540,6 +1540,7 @@ static void *file_ram_alloc(RAMBlock *block,
off_t offset, off_t offset,
Error **errp) Error **errp)
{ {
uint32_t qemu_map_flags;
void *area; void *area;
block->page_size = qemu_fd_getpagesize(fd); block->page_size = qemu_fd_getpagesize(fd);
@ -1587,9 +1588,10 @@ static void *file_ram_alloc(RAMBlock *block,
perror("ftruncate"); perror("ftruncate");
} }
area = qemu_ram_mmap(fd, memory, block->mr->align, readonly, qemu_map_flags = readonly ? QEMU_MAP_READONLY : 0;
block->flags & RAM_SHARED, block->flags & RAM_PMEM, qemu_map_flags |= (block->flags & RAM_SHARED) ? QEMU_MAP_SHARED : 0;
offset); qemu_map_flags |= (block->flags & RAM_PMEM) ? QEMU_MAP_SYNC : 0;
area = qemu_ram_mmap(fd, memory, block->mr->align, qemu_map_flags, offset);
if (area == MAP_FAILED) { if (area == MAP_FAILED) {
error_setg_errno(errp, errno, error_setg_errno(errp, errno,
"unable to map backing store for guest RAM"); "unable to map backing store for guest RAM");

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@ -118,9 +118,12 @@ static void *mmap_reserve(size_t size, int fd)
* Activate memory in a reserved region from the given fd (if any), to make * Activate memory in a reserved region from the given fd (if any), to make
* it accessible. * it accessible.
*/ */
static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly, static void *mmap_activate(void *ptr, size_t size, int fd,
bool shared, bool is_pmem, off_t map_offset) uint32_t qemu_map_flags, off_t map_offset)
{ {
const bool readonly = qemu_map_flags & QEMU_MAP_READONLY;
const bool shared = qemu_map_flags & QEMU_MAP_SHARED;
const bool sync = qemu_map_flags & QEMU_MAP_SYNC;
const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE); const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
int map_sync_flags = 0; int map_sync_flags = 0;
int flags = MAP_FIXED; int flags = MAP_FIXED;
@ -128,7 +131,7 @@ static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly,
flags |= fd == -1 ? MAP_ANONYMOUS : 0; flags |= fd == -1 ? MAP_ANONYMOUS : 0;
flags |= shared ? MAP_SHARED : MAP_PRIVATE; flags |= shared ? MAP_SHARED : MAP_PRIVATE;
if (shared && is_pmem) { if (shared && sync) {
map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
} }
@ -173,9 +176,7 @@ static inline size_t mmap_guard_pagesize(int fd)
void *qemu_ram_mmap(int fd, void *qemu_ram_mmap(int fd,
size_t size, size_t size,
size_t align, size_t align,
bool readonly, uint32_t qemu_map_flags,
bool shared,
bool is_pmem,
off_t map_offset) off_t map_offset)
{ {
const size_t guard_pagesize = mmap_guard_pagesize(fd); const size_t guard_pagesize = mmap_guard_pagesize(fd);
@ -199,7 +200,7 @@ void *qemu_ram_mmap(int fd,
offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; 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, qemu_map_flags,
map_offset); map_offset);
if (ptr == MAP_FAILED) { if (ptr == MAP_FAILED) {
munmap(guardptr, total); munmap(guardptr, total);

View File

@ -229,8 +229,9 @@ void *qemu_memalign(size_t alignment, size_t size)
/* alloc shared memory pages */ /* alloc shared memory pages */
void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared) void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
{ {
const uint32_t qemu_map_flags = shared ? QEMU_MAP_SHARED : 0;
size_t align = QEMU_VMALLOC_ALIGN; 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, qemu_map_flags, 0);
if (ptr == MAP_FAILED) { if (ptr == MAP_FAILED) {
return NULL; return NULL;