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b=DUvShgphV0HpF8KYUua/9LLKbfqc0fbegRrwSjbUVn8A+OnM+potPJQzEPd0AYvZE MNFpBkNbD+DI6mtpj7p1nPmcXc5CID91D0KNIUGpZfxZF3bMpr50ncdpBsSu5QcyE8 xpDyqp+/2twCyV2kWaafcU9i108LC9rfGMSswE+Cq4YQ7eMGE9Si1+X9HQ7/96M1sG KpNpLeG/bLIP8LvGFJDg3tQY4UOM/2Tg5AKwlSWxumQ6m1OzUSa9EWN65ImCPHhE3r vy4TFapDE2nVXoLvxD5YGsLEK+5mpfUZl3wi4XsYdwKBtIy9rPYzP27yjbh+xqGkua 6xmdlIDXwNy1g== From: Pratyush Yadav To: Mike Rapoport , Pasha Tatashin , Pratyush Yadav , Alexander Graf , Muchun Song , Oscar Salvador , David Hildenbrand , Andrew Morton , Jason Miu , Jork Loeser Cc: kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v5 03/22] kho: disallow wide keys in radix tree Date: Wed, 29 Jul 2026 16:55:48 +0200 Message-ID: <20260729145610.2827231-4-pratyush@kernel.org> X-Mailer: git-send-email 2.55.0.508.g3f0d502094-goog In-Reply-To: <20260729145610.2827231-1-pratyush@kernel.org> References: <20260729145610.2827231-1-pratyush@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 28BD080006 X-Stat-Signature: zd6rrwzpat3ins3ccxnib6qbufs8act9 X-Rspam-User: X-HE-Tag: 1785336990-200453 X-HE-Meta: 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 ReMwg85p wwDWLKmnHlpNLZKmmw0G0HCFgIZ4z2Wev06Nx4dQNlZIRicAepDMer5IW0l5j7rpGHgCBmN9UvoZF3YG3k9CD+k+r/kW/nZJ1t69dTyLsvYfhP1qbO9g6H4dpIyJHdoH6B91lPwnLxcTXjI526Kb1Bb+nYNvwD6eaHySdanm4Gtlu/qGSHsKhTSthkUWP/rmy+jX6OByocM7oMkTa4PCrMUGgqCn9ejFId3uh+sLqvKV8Rgg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: "Pratyush Yadav (Google)" The KHO radix tree was designed to track preserved pages. So it does not provide the capability to track any 64-bit key. Instead, it limits the key width to how much it needs for tracking PFNs and their orders. Limiting the width reduces the number of levels in the tree. KHO is not expected to be the only user of the radix tree. With the API generalized to allow other users, now it is possible to add any key to the tree. Check the key width at kho_radix_add_key(), and error out if it exceeds what the tree can handle. Do this instead of increasing the tree depth since right now there are no users that need to use wider keys, so this avoids memory overhead and ABI breakage. Signed-off-by: Pratyush Yadav (Google) --- kernel/liveupdate/kexec_handover.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index ea24f23ce292..e7451743b87e 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -156,6 +156,11 @@ static unsigned long kho_radix_get_table_index(unsigned long key, * intermediate nodes do not exist along the path, they are allocated and added * to the tree. * + * NOTE: Currently only keys of width up to %KHO_RADIX_KEY_WIDTH are supported. + * This limit only exists because current users of the radix tree don't use more + * than that. Changing the maximum width requires changing the tree depth, which + * needs bumping the ABI version. + * * Return: 0 on success, or a negative error code on failure. */ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key) @@ -172,6 +177,9 @@ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key) if (WARN_ON_ONCE(!tree->root)) return -EINVAL; + if (unlikely(fls64(key) > KHO_RADIX_KEY_WIDTH)) + return -ERANGE; + might_sleep(); guard(mutex)(&tree->lock); @@ -244,6 +252,10 @@ void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key) if (WARN_ON_ONCE(!tree->root)) return; + /* Keys wider than KHO_RADIX_KEY_WIDTH are not allowed to be added. */ + if (unlikely(fls64(key) > KHO_RADIX_KEY_WIDTH)) + return; + might_sleep(); guard(mutex)(&tree->lock); -- 2.55.0.508.g3f0d502094-goog