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util/mmap-alloc: fix hugetlb support on ppc64

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Since commit 8561c9244d "exec: allocate PROT_NONE pages on top of
RAM", it is no longer possible to back guest RAM with hugepages on ppc64
hosts:

mmap(NULL, 285212672, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x3fff57000000
mmap(0x3fff57000000, 268435456, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED, 19, 0) = -1 EBUSY (Device or resource busy)

This is because on ppc64, Linux fixes a page size for a virtual address
at mmap time, so we can't switch a range of memory from anonymous
small pages to hugetlbs with MAP_FIXED.

See commit d0f13e3c20b6fb73ccb467bdca97fa7cf5a574cd
("[POWERPC] Introduce address space "slices"") in Linux
history for the details.

Detect this and create the PROT_NONE mapping using the same fd.

Naturally, this makes the guard page bigger with hugetlbfs.

Based on patch by Greg Kurz.

Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2015-12-02 21:14:12 +02:00
parent 0560b0e97d
commit 7197fb4058
3 changed files with 42 additions and 23 deletions
Download patch file Download diff file Expand all files Collapse all files

39
util/mmap-alloc.c
View file

@ -14,6 +14,32 @@
#include <sys/mman.h>
#include <assert.h>
#define HUGETLBFS_MAGIC 0x958458f6
#ifdef CONFIG_LINUX
#include <sys/vfs.h>
#endif
size_t qemu_fd_getpagesize(int fd)
{
#ifdef CONFIG_LINUX
struct statfs fs;
int ret;
if (fd != -1) {
do {
ret = fstatfs(fd, &fs);
} while (ret != 0 && errno == EINTR);
if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
return fs.f_bsize;
}
}
#endif
return getpagesize();
}
void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
{
/*
@ -21,7 +47,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
* space, even if size is already aligned.
*/
size_t total = size + align;
#if defined(__powerpc64__) && defined(__linux__)
/* On ppc64 mappings in the same segment (aka slice) must share the same
* page size. Since we will be re-allocating part of this segment
* from the supplied fd, we should make sure to use the same page size,
* unless we are using the system page size, in which case anonymous memory
* is OK. Use align as a hint for the page size.
* In this case, set MAP_NORESERVE to avoid allocating backing store memory.
*/
int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
#else
void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
#endif
size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
void *ptr1;