+ kho-warn-and-exit-when-unpreserved-page-wasnt-preserved.patch added to mm-hotfixes-unstable branch

+ kho-warn-and-exit-when-unpreserved-page-wasnt-preserved.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: kho: warn and exit when unpreserved page wasn't preserved
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     kho-warn-and-exit-when-unpreserved-page-wasnt-preserved.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kho-warn-and-exit-when-unpreserved-page-wasnt-preserved.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Pratyush Yadav <pratyush@kernel.org>
Subject: kho: warn and exit when unpreserved page wasn't preserved
Date: Mon, 3 Nov 2025 19:02:32 +0100

Calling __kho_unpreserve() on a pair of (pfn, end_pfn) that wasn't
preserved is a bug.  Currently, if that is done, the physxa or bits can be
NULL.  This results in a soft lockup since a NULL physxa or bits results
in redoing the loop without ever making any progress.

Return when physxa or bits are not found, but WARN first to loudly
indicate invalid behaviour.

Link: https://lkml.kernel.org/r/20251103180235.71409-3-pratyush@kernel.org
Fixes: fc33e4b44b271 ("kexec: enable KHO support for memory preservation")
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/kexec_handover.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/kexec_handover.c~kho-warn-and-exit-when-unpreserved-page-wasnt-preserved
+++ a/kernel/kexec_handover.c
@@ -171,12 +171,12 @@ static void __kho_unpreserve(struct kho_
 		const unsigned long pfn_high = pfn >> order;
 
 		physxa = xa_load(&track->orders, order);
-		if (!physxa)
-			continue;
+		if (WARN_ON_ONCE(!physxa))
+			return;
 
 		bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
-		if (!bits)
-			continue;
+		if (WARN_ON_ONCE(!bits))
+			return;
 
 		clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
 
_

Patches currently in -mm which might be from pratyush@kernel.org are

kho-fix-out-of-bounds-access-of-vmalloc-chunk.patch
kho-fix-unpreservation-of-higher-order-vmalloc-preservations.patch
kho-warn-and-exit-when-unpreserved-page-wasnt-preserved.patch