Message ID | 20210319101230.21531-10-david@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | RAM_NORESERVE, MAP_NORESERVE and hostmem "reserve" property | expand |
On Fri, Mar 19, 2021 at 11:12:25AM +0100, David Hildenbrand wrote: > 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. > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > include/qemu/mmap-alloc.h | 16 +++++++++------- > include/qemu/osdep.h | 18 ++++++++++++++++++ > softmmu/physmem.c | 8 +++++--- > util/mmap-alloc.c | 15 ++++++++------- > util/oslib-posix.c | 3 ++- > 5 files changed, 42 insertions(+), 18 deletions(-) > > diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h > index 456ff87df1..a60a2085b3 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 ^ | +---- underscore > + * implicitly based on other parameters. > + * Reviewed-by: Peter Xu <peterx@redhat.com>
On 23.03.21 21:49, Peter Xu wrote: > On Fri, Mar 19, 2021 at 11:12:25AM +0100, David Hildenbrand wrote: >> 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. >> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> include/qemu/mmap-alloc.h | 16 +++++++++------- >> include/qemu/osdep.h | 18 ++++++++++++++++++ >> softmmu/physmem.c | 8 +++++--- >> util/mmap-alloc.c | 15 ++++++++------- >> util/oslib-posix.c | 3 ++- >> 5 files changed, 42 insertions(+), 18 deletions(-) >> >> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h >> index 456ff87df1..a60a2085b3 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 > ^ > | > +---- underscore > Nice catch, thanks :)
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h index 456ff87df1..a60a2085b3 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 ba15be9c56..5ba89f5460 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -347,6 +347,24 @@ 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) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index fdcd38ba61..d1a1a6b72e 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 qemu_map_flags; void *area; block->page_size = qemu_fd_getpagesize(fd); @@ -1580,9 +1581,10 @@ static void *file_ram_alloc(RAMBlock *block, perror("ftruncate"); } - area = qemu_ram_mmap(fd, memory, block->mr->align, readonly, - block->flags & RAM_SHARED, block->flags & RAM_PMEM, - offset); + qemu_map_flags = readonly ? QEMU_MAP_READONLY : 0; + qemu_map_flags |= (block->flags & RAM_SHARED) ? QEMU_MAP_SHARED : 0; + 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) { 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..1ddc0e2a1e 100644 --- a/util/mmap-alloc.c +++ b/util/mmap-alloc.c @@ -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 * it accessible. */ -static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly, - bool shared, bool is_pmem, off_t map_offset) +static void *mmap_activate(void *ptr, size_t size, int fd, + 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); int map_sync_flags = 0; 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 |= shared ? MAP_SHARED : MAP_PRIVATE; - if (shared && is_pmem) { + if (shared && sync) { 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, size_t size, size_t align, - bool readonly, - bool shared, - bool is_pmem, + uint32_t qemu_map_flags, off_t map_offset) { 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; - ptr = mmap_activate(guardptr + offset, size, fd, readonly, shared, is_pmem, + ptr = mmap_activate(guardptr + offset, size, fd, qemu_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..c12108c6cb 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 qemu_map_flags = shared ? QEMU_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, qemu_map_flags, 0); if (ptr == MAP_FAILED) { return NULL;
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. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/qemu/mmap-alloc.h | 16 +++++++++------- include/qemu/osdep.h | 18 ++++++++++++++++++ softmmu/physmem.c | 8 +++++--- util/mmap-alloc.c | 15 ++++++++------- util/oslib-posix.c | 3 ++- 5 files changed, 42 insertions(+), 18 deletions(-)