From 7197fb4058bcb68986bae2bb2c04d6370f3e7218 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Wed, 2 Dec 2015 21:14:12 +0200 Subject: util/mmap-alloc: fix hugetlb support on ppc64 Since commit 8561c9244ddf1122d "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 Reviewed-by: Greg Kurz Tested-by: Greg Kurz Signed-off-by: Michael S. Tsirkin --- util/mmap-alloc.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'util/mmap-alloc.c') diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c index c37acbe..54793a5 100644 --- a/util/mmap-alloc.c +++ b/util/mmap-alloc.c @@ -14,6 +14,32 @@ #include #include +#define HUGETLBFS_MAGIC 0x958458f6 + +#ifdef CONFIG_LINUX +#include +#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; -- cgit v1.1