util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve()
We want to reserve a memory region without actually populating memory. Let's factor that out. Reviewed-by: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com> Acked-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> 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: <20210510114328.21835-3-david@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -82,6 +82,38 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
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return qemu_real_host_page_size;
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return qemu_real_host_page_size;
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}
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}
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/*
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* Reserve a new memory region of the requested size to be used for mapping
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* from the given fd (if any).
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*/
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static void *mmap_reserve(size_t size, int fd)
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{
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int flags = MAP_PRIVATE;
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#if defined(__powerpc64__) && defined(__linux__)
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/*
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* On ppc64 mappings in the same segment (aka slice) must share the same
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* page size. Since we will be re-allocating part of this segment
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* from the supplied fd, we should make sure to use the same page size, to
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* this end we mmap the supplied fd. In this case, set MAP_NORESERVE to
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* avoid allocating backing store memory.
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* We do this unless we are using the system page size, in which case
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* anonymous memory is OK.
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*/
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if (fd == -1 || qemu_fd_getpagesize(fd) == qemu_real_host_page_size) {
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fd = -1;
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flags |= MAP_ANONYMOUS;
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} else {
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flags |= MAP_NORESERVE;
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}
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#else
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fd = -1;
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flags |= MAP_ANONYMOUS;
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#endif
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return mmap(0, size, PROT_NONE, flags, fd, 0);
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}
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static inline size_t mmap_guard_pagesize(int fd)
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static inline size_t mmap_guard_pagesize(int fd)
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{
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{
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#if defined(__powerpc64__) && defined(__linux__)
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#if defined(__powerpc64__) && defined(__linux__)
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@ -104,7 +136,6 @@ void *qemu_ram_mmap(int fd,
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int prot;
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int prot;
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int flags;
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int flags;
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int map_sync_flags = 0;
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int map_sync_flags = 0;
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int guardfd;
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size_t offset;
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size_t offset;
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size_t total;
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size_t total;
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void *guardptr;
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void *guardptr;
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@ -116,30 +147,7 @@ void *qemu_ram_mmap(int fd,
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*/
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*/
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total = size + align;
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total = size + align;
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#if defined(__powerpc64__) && defined(__linux__)
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guardptr = mmap_reserve(total, fd);
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/* On ppc64 mappings in the same segment (aka slice) must share the same
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* page size. Since we will be re-allocating part of this segment
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* from the supplied fd, we should make sure to use the same page size, to
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* this end we mmap the supplied fd. In this case, set MAP_NORESERVE to
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* avoid allocating backing store memory.
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* We do this unless we are using the system page size, in which case
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* anonymous memory is OK.
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*/
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flags = MAP_PRIVATE;
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if (fd == -1 || guard_pagesize == qemu_real_host_page_size) {
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guardfd = -1;
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flags |= MAP_ANONYMOUS;
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} else {
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guardfd = fd;
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flags |= MAP_NORESERVE;
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}
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#else
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guardfd = -1;
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flags = MAP_PRIVATE | MAP_ANONYMOUS;
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#endif
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guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0);
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if (guardptr == MAP_FAILED) {
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if (guardptr == MAP_FAILED) {
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return MAP_FAILED;
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return MAP_FAILED;
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}
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}
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