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b=VIr0rjstKJ3saWpOlCPEj9yrlsSRfWVdSQkR1q6I3ZgbEqEbjPhjAwZARfKCLBEHD NGXFco0t56DpoMlRyxC4Dv7YU5Dj77k5L5LEk+YeLgg6BmGF3YD/hglGfiBsfuYSL3 WalSNO2wr0gm3B+obfSK4LBPcORjuDCqoqCbXgpv9hONWBGRCQH7Icr1ATqy0Pmb9r ZMVa4ISTLJXD4HD0aPUFJ3/8+8HfJoZY1kBU/TJZKi4MwFDa1g7A0PisLusFC0HKNg wdLEn1kFzdFK2Tk27NHIoXVG5ZbkwxsahhpJX0ykb16FldNGhAL4Y2Sxc+/7dRi/YV dht9+6EHugDgQ== Date: Thu, 13 Nov 2025 13:39:26 +0200 From: Mike Rapoport To: Mehdi Ben Hadj Khelifa Cc: akpm@linux-foundation.org, peterx@redhat.com, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, shuah@kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, david.hunter.linux@gmail.com, khalid@kernel.org, linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [PATCH] selftests/mm/uffd: remove static address usage in shmem_allocate_area() Message-ID: References: <20251111205739.420009-1-mehdi.benhadjkhelifa@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251111205739.420009-1-mehdi.benhadjkhelifa@gmail.com> X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 55DC640014 X-Stat-Signature: j3i6sehnbcsb3r64dzcup4k1c3asr8go X-HE-Tag: 1763033977-92873 X-HE-Meta: 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 fZBVytV2 DdBUSWgaxNL2kNJoioIQ4K2lavZn009HmU0GpLg6IKopcLPZewRgRND5k8dTBtNxCl8iTGSymmeBDGXE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Nov 11, 2025 at 09:54:27PM +0100, Mehdi Ben Hadj Khelifa wrote: > The current shmem_allocate_area() implementation uses a hardcoded virtual > base address(BASE_PMD_ADDR) as a hint for mmap() when creating shmem-backed > test areas. This approach is fragile and may fail on systems with ASLR or > different virtual memory layouts, where the chosen address is unavailable. > > Replace the static base address with a dynamically reserved address range > obtained via mmap(NULL, ..., PROT_NONE). The memfd-backed areas and their > alias are then mapped into that reserved region using MAP_FIXED, preserving > the original layout and aliasing semantics while avoiding collisions with > unrelated mappings. > > This change improves robustness and portability of the test suite without > altering its behavior or coverage. > > Signed-off-by: Mehdi Ben Hadj Khelifa > --- > Testing: > A diff between running the mm selftests on 6.18-rc5 from before and after > the change show no regression on x86_64 architecture with 32GB DDR5 RAM. > tools/testing/selftests/mm/uffd-common.c | 25 +++++++++++++++--------- > 1 file changed, 16 insertions(+), 9 deletions(-) > > diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c > index 994fe8c03923..492b21c960bb 100644 > --- a/tools/testing/selftests/mm/uffd-common.c > +++ b/tools/testing/selftests/mm/uffd-common.c > @@ -6,11 +6,11 @@ > */ > > #include "uffd-common.h" > +#include "asm-generic/mman-common.h" Please drop this. There's already include via uffd-common.h/vm_util.h. > > uffd_test_ops_t *uffd_test_ops; > uffd_test_case_ops_t *uffd_test_case_ops; > > -#define BASE_PMD_ADDR ((void *)(1UL << 30)) > > /* pthread_mutex_t starts at page offset 0 */ > pthread_mutex_t *area_mutex(char *area, unsigned long nr, uffd_global_test_opts_t *gopts) > @@ -142,30 +142,37 @@ static int shmem_allocate_area(uffd_global_test_opts_t *gopts, void **alloc_area > unsigned long offset = is_src ? 0 : bytes; > char *p = NULL, *p_alias = NULL; > int mem_fd = uffd_mem_fd_create(bytes * 2, false); > + size_t region_size = bytes * 2 + hpage_size; > > - /* TODO: clean this up. Use a static addr is ugly */ > - p = BASE_PMD_ADDR; > - if (!is_src) > - /* src map + alias + interleaved hpages */ > - p += 2 * (bytes + hpage_size); > + void *reserve = mmap(NULL, region_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, > + -1, 0); > + if (reserve == MAP_FAILED) { > + close(mem_fd); > + return -errno; > + } > + > + p = (char *)reserve; No need for casting here. > p_alias = p; > p_alias += bytes; > p_alias += hpage_size; /* Prevent src/dst VMA merge */ > > - *alloc_area = mmap(p, bytes, PROT_READ | PROT_WRITE, MAP_SHARED, > + *alloc_area = mmap(p, bytes, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED, > mem_fd, offset); > if (*alloc_area == MAP_FAILED) { > + munmap(reserve, region_size); I think it'll be more readable to put munmap() after setting *alloc_area to NULL. > *alloc_area = NULL; > + close(mem_fd); > return -errno; > } > if (*alloc_area != p) > err("mmap of memfd failed at %p", p); > > - area_alias = mmap(p_alias, bytes, PROT_READ | PROT_WRITE, MAP_SHARED, > + area_alias = mmap(p_alias, bytes, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED, > mem_fd, offset); > if (area_alias == MAP_FAILED) { > - munmap(*alloc_area, bytes); > + munmap(reserve, region_size); Here as well. > *alloc_area = NULL; > + close(mem_fd); > return -errno; > } > if (area_alias != p_alias) > -- > 2.51.2 > -- Sincerely yours, Mike.