linux-kernel - [PATCH 2/2] kho: warn and exit when unpreserved page wasn't preserved

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Message-ID: <20251103180235.71409-3-pratyush@kernel.org>
Date: Mon,  3 Nov 2025 19:02:32 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>,
	Alexander Graf <graf@...zon.com>,
	Mike Rapoport <rppt@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Pratyush Yadav <pratyush@...nel.org>
Cc: kexec@...ts.infradead.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] kho: warn and exit when unpreserved page wasn't preserved

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.

Fixes: fc33e4b44b271 ("kexec: enable KHO support for memory preservation")
Signed-off-by: Pratyush Yadav <pratyush@...nel.org>
---
 kernel/kexec_handover.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index c2bcbb10918ce..e5fd833726226 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -167,12 +167,12 @@ static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
 		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);
 
-- 
2.47.3