linux-kernel - [PATCH] arm64: mm: Correct the update of max

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Message-ID: <20250321070019.1271859-1-quic_zhenhuah@quicinc.com>
Date: Fri, 21 Mar 2025 15:00:19 +0800
From: Zhenhua Huang <quic_zhenhuah@...cinc.com>
To: <anshuman.khandual@....com>, <catalin.marinas@....com>, <david@...hat.com>,
        <will@...nel.org>, <ryan.roberts@....com>, <mark.rutland@....com>,
        <ardb@...nel.org>, <quic_zhenhuah@...cinc.com>,
        <yangyicong@...ilicon.com>, <joey.gouly@....com>,
        <quic_cgoldswo@...cinc.com>, <quic_sudaraja@...cinc.com>,
        <akpm@...ux-foundation.org>
CC: <linux-mm@...ck.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <quic_tingweiz@...cinc.com>
Subject: [PATCH] arm64: mm: Correct the update of max_pfn

Hotplugged memory can be smaller than the original memory. For example,
on my target:

root@...ericarmv8:~# cat /sys/kernel/debug/memblock/memory
   0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
   1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
   2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
   3: 0x0000000088800000..0x0000000094ffefff    0 NONE
   4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
max_pfn will affect read_page_owner. Therefore, it should first compare and
then select the larger value for max_pfn.

Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
---
 arch/arm64/mm/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 1dfe1a8efdbe..310ff75891ef 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
 		__remove_pgd_mapping(swapper_pg_dir,
 				     __phys_to_virt(start), size);
 	else {
-		max_pfn = PFN_UP(start + size);
+		/* Address of hotplugged memory can be smaller */
+		max_pfn = max(max_pfn, PFN_UP(start + size));
 		max_low_pfn = max_pfn;
 	}
 
-- 
2.25.1