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6e4c890e15
1st mmap returns *ptr* which aligns to host page size,
| size + align |
------------------------------------------
ptr
input param *align* could be 1M, or 2M, or host page size. After
QEMU_ALIGN_UP, offset will >= 0
2nd mmap use flag MAP_FIXED, then it return ptr+offset, or else fail.
If it success, then we will have something like:
| offset | size |
--------------------------------------
ptr ptr1
*ptr1* is what we really want to return, it equals ptr+offset.
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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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#define HUGETLBFS_MAGIC 0x958458f6
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#ifdef CONFIG_LINUX
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#include <sys/vfs.h>
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#endif
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size_t qemu_fd_getpagesize(int fd)
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{
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#ifdef CONFIG_LINUX
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struct statfs fs;
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int ret;
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if (fd != -1) {
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do {
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ret = fstatfs(fd, &fs);
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} while (ret != 0 && errno == EINTR);
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if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
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return fs.f_bsize;
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}
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}
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#endif
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return getpagesize();
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}
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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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/*
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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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size_t 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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int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
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int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
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void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
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#else
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void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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#endif
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size_t offset;
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void *ptr1;
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if (ptr == MAP_FAILED) {
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return MAP_FAILED;
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}
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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 >= getpagesize());
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offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
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ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
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MAP_FIXED |
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(fd == -1 ? MAP_ANONYMOUS : 0) |
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(shared ? MAP_SHARED : MAP_PRIVATE),
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fd, 0);
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if (ptr1 == MAP_FAILED) {
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munmap(ptr, total);
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return MAP_FAILED;
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}
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if (offset > 0) {
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munmap(ptr, 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 + getpagesize()) {
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munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
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}
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return ptr1;
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}
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void qemu_ram_munmap(void *ptr, size_t size)
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{
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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munmap(ptr, size + getpagesize());
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}
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}
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