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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 v8 22/30] mm/madvise: keep PMD swap entries whole for MADV_GUARD_INSTALL/REMOVE Date: Fri, 2 Oct 2026 02:52:36 -0700 Message-ID: <20261002095503.3585565-23-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261002095503.3585565-1-usama.arif@linux.dev> References: <20261002095503.3585565-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: uspqiztfts7ayry74pitkz3tpeuypxwp X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 972E840002 X-HE-Tag: 1790935038-202820 X-HE-Meta: U2FsdGVkX1+3ymPV9LFEhwmLCpzPx+fT29Z/De8U9snAIhSV8N0pghlUlWw7vNAKMCuDKB23/+Yg/8qHVnRT/dkiyzZXlFHIfXpyJKtewvIb9uJLCIBbhtwXR4AEWYXWTW4AcFUXn59whNyEHHLNZebYJ+59ezXibpkLaBpwCMCMjKFanU++FOhWON/fsiVRpqPfI3Qf6Alem1HhxDQx9/teCJXUHZ1upvx12Eo+toKnY2obyPo/Vglfe6t6WMw90AFD/0Q22gdWHaS5ED7BBMaVMZ0RvBEZ0NrT6wjK3aHNZHIag/0ghxomzsz/tKaefrR3mWMUISsevUPt2yelQPSGrZ07e94coMeWxEfd52OqpxTsdxkhUpQpwFfTqR/hxqzuoQs0e5A2GiLmPpVAH4dWZqCQvxyn+t07tF9tTOUvQO3wP1nqrT4a0c2INpj1dD4NB8Y8ipdBAn+qhMR/P8s3WLk3MwWfgpXFuMt3/7CoPCjZalCnDVeK7kDsjJkDqXmkrFhjHj3r+2kJ4quhsdz5vF0AuWMgMwKOFYSmOi0N39B99HcbkWmTr9xArlU5bel3RKSk1pDv9l7T6BVmo51GHi7YoLtGWGEWbNhDk6VyjwwFvmBTB2tmqNz1dhnNB4xbvfMvTRDE8osy4gKWJj60hqmGdW0tcPRiqm1Yw0vAyrszzXaSQ3qep2tCEhrHyNR+TW1SrxSPlWq6S/rivhX4Vflm3+RIEnAvn1jaXfJRCWEVcuNJPss62Ay3PPujXaTrAjtrZH58iZnmvlaaTzPHdbCRuFdxJ4CfaP6Y3lsMUWHnKbn1YuRJ+mJweRla08y7A/cSv8mnH0GAyxaZYPhty5Nn/54d3Z3fxqoGbby7tbn173oDrA8iEk+6hY7ST5XnGdY6HSMxvDMLIF2ekBeoNsk8Zz7ExXRLiiqeeWg3pansBwjDSACk3ac4tx9UD/6QckfS1TZ0YbXkQxX UAyb/ghr aQ1DikFs4iU0koMNfL7hndvdqSpxFKV8bG0a0ZrRR0laVBCaEm4Q2EwdWsYYa3TqD+Kdnn+XDyQbI1VIkv4raLXLtu0Vdq5v+xHrYt4EMoBqV8QC3uiLGyZ7FIEI1CwFp3EM8zY1V8RRYq1S7nLsso8S5Sfg1DVLVeqkvpYTrkh80wFPt3QIO/O1hpCbz4hObL0sF8eq0nVXHy5gLCh++zyCoJz+2lt1zoLUciKQA46sw00DjA7NPQDORo0L7l79KqATxLESUaHfiNJO5+tcYpkT6eQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 d3b5ed7e3cffb..64019668d69fb 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1269,8 +1269,12 @@ 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, @@ -1409,8 +1413,12 @@ 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