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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v9 24/32] mm/madvise: keep PMD swap entries whole for MADV_GUARD_INSTALL/REMOVE Date: Thu, 5 Nov 2026 10:39:08 -0800 Message-ID: <20261105183940.2236717-25-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261105183940.2236717-1-usama.arif@linux.dev> References: <20261105183940.2236717-1-usama.arif@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Both callbacks test bare pmd_trans_huge(), which is false for a PMD swap entry, so they return without consuming the PMD and walk_pmd_range() splits it - only for the PTE callbacks to find the range populated and abort, or to find no guard markers and do nothing. Both already short-circuit at PMD level for a present THP. Do the same for a swapped-out one: it is just as populated, and just as free of guard markers. Signed-off-by: Usama Arif --- mm/madvise.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 576707e303cf2..f7f17efdd926d 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1109,8 +1109,12 @@ static int guard_install_pmd_entry(pmd_t *pmd, unsigned long addr, { pmd_t pmdval = pmdp_get(pmd); - /* If huge return >0 so we abort the operation + zap. */ - return pmd_trans_huge(pmdval); + /* + * If huge return >0 so we abort the operation + zap. A PMD swap entry + * is a swapped-out THP: also populated, and splitting it here would + * only demote it before the zap. + */ + return pmd_trans_huge(pmdval) || pmd_is_swap_entry(pmdval); } static int guard_install_pte_entry(pte_t *pte, unsigned long addr, @@ -1249,8 +1253,12 @@ static int guard_remove_pmd_entry(pmd_t *pmd, unsigned long addr, { pmd_t pmdval = pmdp_get(pmd); - /* If huge, cannot have guard pages present, so no-op - skip. */ - if (pmd_trans_huge(pmdval)) + /* + * If huge, cannot have guard pages present, so no-op - skip. The same + * is true of a PMD swap entry, which must not be split just to discover + * there is nothing to remove. + */ + if (pmd_trans_huge(pmdval) || pmd_is_swap_entry(pmdval)) walk->action = ACTION_CONTINUE; return 0; -- 2.53.0-Meta