From: "Kirill A. Shutemov" kirill@shutemov.name Subject: mm/shmem.c: thp, shmem: fix conflict of above-47bit hint address and PMD alignment
Shmem/tmpfs tries to provide THP-friendly mappings if huge pages are enabled. But it doesn't work well with above-47bit hint address.
Normally, the kernel doesn't create userspace mappings above 47-bit, even if the machine allows this (such as with 5-level paging on x86-64). Not all user space is ready to handle wide addresses. It's known that at least some JIT compilers use higher bits in pointers to encode their information.
Userspace can ask for allocation from full address space by specifying hint address (with or without MAP_FIXED) above 47-bits. If the application doesn't need a particular address, but wants to allocate from whole address space it can specify -1 as a hint address.
Unfortunately, this trick breaks THP alignment in shmem/tmp: shmem_get_unmapped_area() would not try to allocate PMD-aligned area if *any* hint address specified.
This can be fixed by requesting the aligned area if the we failed to allocated at user-specified hint address. The request with inflated length will also take the user-specified hint address. This way we will not lose an allocation request from the full address space.
[kirill@shutemov.name: fold in a fixup] Link: http://lkml.kernel.org/r/20191223231309.t6bh5hkbmokihpfu@box Link: http://lkml.kernel.org/r/20191220142548.7118-3-kirill.shutemov@linux.intel.c... Fixes: b569bab78d8d ("x86/mm: Prepare to expose larger address space to userspace") Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: "Willhalm, Thomas" thomas.willhalm@intel.com Cc: Dan Williams dan.j.williams@intel.com Cc: "Bruggeman, Otto G" otto.g.bruggeman@intel.com Cc: "Aneesh Kumar K . V" aneesh.kumar@linux.vnet.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/shmem.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/mm/shmem.c~thp-shmem-fix-conflict-of-above-47bit-hint-address-and-pmd-alignment +++ a/mm/shmem.c @@ -2107,9 +2107,10 @@ unsigned long shmem_get_unmapped_area(st /* * Our priority is to support MAP_SHARED mapped hugely; * and support MAP_PRIVATE mapped hugely too, until it is COWed. - * But if caller specified an address hint, respect that as before. + * But if caller specified an address hint and we allocated area there + * successfully, respect that as before. */ - if (uaddr) + if (uaddr == addr) return addr;
if (shmem_huge != SHMEM_HUGE_FORCE) { @@ -2143,7 +2144,7 @@ unsigned long shmem_get_unmapped_area(st if (inflated_len < len) return addr;
- inflated_addr = get_area(NULL, 0, inflated_len, 0, flags); + inflated_addr = get_area(NULL, uaddr, inflated_len, 0, flags); if (IS_ERR_VALUE(inflated_addr)) return addr; if (inflated_addr & ~PAGE_MASK) _