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b=ANlFB3KdmGzi6pRPz/Msov+nrcs+dWmK2IqxUKObhB61zauElfiUr1UU7ct9t6nqV nnGxLC+uyoz35YrNU0U7ucFPGn5WdCgU3dB1+NAPf/KRBwj+BoZSGUZDgRuKbbn2Nk n586FtCTMEYY15fU08udtoAB5JdYmyiiG6bQdi7zhzqq+4QlJBLBG5PFPx+vNmB01Z ndTghWSxlJ/eNyMr4uZGhNvCaD7nfRRgOilnnh4bO8FS6VtKCQTVp4CD5IWbfd7QWP V9uOK3ldMMyng+FvbS4mcsqcq4fYWbnrWBzUCjvfK7j12aaF4way83aTHQYgFRkst7 +R/ej7dlhrZwQ== Date: Thu, 13 Nov 2025 18:46:15 +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 v2] selftests/mm/uffd: remove static address usage in shmem_allocate_area() Message-ID: References: <20251113142050.108638-1-mehdi.benhadjkhelifa@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251113142050.108638-1-mehdi.benhadjkhelifa@gmail.com> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: CCBD4C000A X-Stat-Signature: 5obbkxr5mh9nza7djud6bwsejrip4unb X-Rspam-User: X-HE-Tag: 1763052385-741547 X-HE-Meta: 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 LAFIB1p2 hyeuWUg31qdpTIpR0avtEL4V/f2Gd4Lmz4ibS8j6RDHgsbtzsz/ShBrrhLYacNuDX/iOCelJCsRPS2Cy7x+uLdM1eu1auE4kSvS36lDZqqmUoW1RSSBdlKsDv05j0JsIp3Z6zJk9iDsSAWBqnIwOlGMLTACdaumP6cugl7xeLQkfxzwwX7gnrkdbLoks4WLQplDBD7Syo7kc6grCD2RETjsc0dzoi6dxlhdVW7JlvPtPLiN0ebzKxlorAYwieByQvTg9/hmye3Iwid+ura9J3mRHB42aBd6nDzddFeL5XiVbcBaolnyezVle+WfdnXtG2KzL9R/vam/zojX1MPA/v5fCBEFskonsUiHOpIkwMKIrNBicnEU9scgE80nQgisAasY+JkSBynB9uznNCaHLbPZOOe890VChq0+ie 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 Thu, Nov 13, 2025 at 03:20:33PM +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. > > Suggested-by: Mike Rapoport > Signed-off-by: Mehdi Ben Hadj Khelifa Reviewed-by: Mike Rapoport (Microsoft) > --- > Testing(Retested): > 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. > > ChangeLog: > > Changes from v1: > > -Implemented Mike's suggestions to make cleanup code more clear. > > Link:https://lore.kernel.org/all/20251111205739.420009-1-mehdi.benhadjkhelifa@gmail.com/ > > tools/testing/selftests/mm/uffd-common.c | 24 +++++++++++++++--------- > 1 file changed, 15 insertions(+), 9 deletions(-) > > diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c > index 994fe8c03923..edd02328f77b 100644 > --- a/tools/testing/selftests/mm/uffd-common.c > +++ b/tools/testing/selftests/mm/uffd-common.c > @@ -10,7 +10,6 @@ > 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 +141,37 @@ 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 = reserve; > 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) { > *alloc_area = NULL; > + munmap(reserve, region_size); > + 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); > *alloc_area = NULL; > + munmap(reserve, region_size); > + close(mem_fd); > return -errno; > } > if (area_alias != p_alias) > -- > 2.51.2 > -- Sincerely yours, Mike.