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0010078e4b
The commit 7197fb4058bcb68986bae2bb2c04d6370f3e7218 ("util/mmap-alloc:
fix hugetlb support on ppc64") fixed Huge TLB mappings on ppc64.
However, we still need to consider the underlying huge page size
during munmap() because it requires that both address and length be a
multiple of the underlying huge page size for Huge TLB mappings.
Quote from "Huge page (Huge TLB) mappings" paragraph under NOTES
section of the munmap(2) manual:
"For munmap(), addr and length must both be a multiple of the
underlying huge page size."
On ppc64, the munmap() in qemu_ram_munmap() does not work for Huge TLB
mappings because the mapped segment can be aligned with the underlying
huge page size, not aligned with the native system page size, as
returned by getpagesize().
This has the side effect of not releasing huge pages back to the pool
after a hugetlbfs file-backed memory device is hot-unplugged.
This patch fixes the situation in qemu_ram_mmap() and
qemu_ram_munmap() by considering the underlying page size on ppc64.
After this patch, memory hot-unplug releases huge pages back to the
pool.
Fixes: 7197fb4058bcb68986bae2bb2c04d6370f3e7218
Backports commit 53adb9d43e1abba187387a51f238e878e934c647 from qemu
110 lines
2.9 KiB
C
110 lines
2.9 KiB
C
/*
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* Support for RAM backed by mmaped host memory.
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*
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* Copyright (c) 2015 Red Hat, Inc.
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*
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* Authors:
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* Michael S. Tsirkin <mst@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qemu/mmap-alloc.h"
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#include "qemu/host-utils.h"
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#include <sys/mman.h>
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void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
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{
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int flags;
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int guardfd;
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size_t offset;
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size_t pagesize;
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size_t total;
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void *guardptr;
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void *ptr;
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/*
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* Note: this always allocates at least one extra page of virtual address
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* space, even if size is already aligned.
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*/
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total = size + align;
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#if defined(__powerpc64__) && defined(__linux__)
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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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pagesize = qemu_fd_getpagesize(fd);
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if (fd == -1 || pagesize == getpagesize()) {
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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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pagesize = getpagesize();
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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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return MAP_FAILED;
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}
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/* Make sure align is a power of 2 */
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assert(is_power_of_2(align));
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/* Always align to host page size */
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assert(align >= pagesize);
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flags = MAP_FIXED;
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flags |= fd == -1 ? MAP_ANONYMOUS : 0;
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flags |= shared ? MAP_SHARED : MAP_PRIVATE;
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offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
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ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, fd, 0);
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if (ptr == MAP_FAILED) {
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munmap(guardptr, total);
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return MAP_FAILED;
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}
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if (offset > 0) {
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munmap(guardptr, offset);
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}
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/*
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* Leave a single PROT_NONE page allocated after the RAM block, to serve as
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* a guard page guarding against potential buffer overflows.
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*/
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total -= offset;
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if (total > size + pagesize) {
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munmap(ptr + size + pagesize, total - size - pagesize);
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}
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return ptr;
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}
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void qemu_ram_munmap(int fd, void *ptr, size_t size)
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{
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size_t pagesize;
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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#if defined(__powerpc64__) && defined(__linux__)
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pagesize = qemu_fd_getpagesize(fd);
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#else
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pagesize = getpagesize();
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#endif
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munmap(ptr, size + pagesize);
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}
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}
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