linux-kernel - [PATCH v4 3/4] x86/mm: Handle alloc failure in phys_*

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Message-ID: <062402c3-e640-4578-b1b1-318a0a728a93@neon.tech>
Date: Fri, 13 Jun 2025 21:11:48 +0100
From: Em Sharnoff <sharnoff@...n.tech>
To: linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org
Cc: Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 Oleg Vasilev <oleg@...n.tech>, Arthur Petukhovsky <arthur@...n.tech>,
 Stefan Radig <stefan@...n.tech>, Misha Sakhnov <misha@...n.tech>
Subject: [PATCH v4 3/4] x86/mm: Handle alloc failure in phys_*_init()

During memory hotplug, allocation failures in phys_*_init() aren't
handled, which results in a null pointer dereference if they occur.

This patch depends on the previous patch ("x86/mm: Allow error returns
from phys_*_init()").

Signed-off-by: Em Sharnoff <sharnoff@...n.tech>
---
Changelog:
- v4: Split this patch out from the error handling changes
---
 arch/x86/mm/init_64.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index b18ab2dcc799..a585daa76d69 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -572,6 +572,8 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr, unsigned long paddr_end,
 		}

 		pte = alloc_low_page();
+		if (!pte)
+			return -ENOMEM;
 		paddr_last = phys_pte_init(pte, paddr, paddr_end, new_prot, init);

 		spin_lock(&init_mm.page_table_lock);
@@ -664,6 +666,8 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
 		}

 		pmd = alloc_low_page();
+		if (!pmd)
+			return -ENOMEM;
 		ret = phys_pmd_init(pmd, paddr, paddr_end,
 				    page_size_mask, prot, init);

@@ -726,6 +730,8 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
 		}

 		pud = alloc_low_page();
+		if (!pud)
+			return -ENOMEM;
 		ret = phys_pud_init(pud, paddr, __pa(vaddr_end),
 				    page_size_mask, prot, init);

@@ -774,6 +780,8 @@ __kernel_physical_mapping_init(unsigned long paddr_start,
 		}

 		p4d = alloc_low_page();
+		if (!p4d)
+			return -ENOMEM;
 		ret = phys_p4d_init(p4d, __pa(vaddr), __pa(vaddr_end),
 				    page_size_mask, prot, init);

-- 
2.39.5