linux-kernel - [RFC PATCH v1 6/6] Revert "arm64/mm: Permit lazy_mmu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250530140446.2387131-7-ryan.roberts@arm.com>
Date: Fri, 30 May 2025 15:04:44 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"David S. Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>,
	Juergen Gross <jgross@...e.com>,
	Ajay Kaher <ajay.kaher@...adcom.com>,
	Alexey Makhalov <alexey.makhalov@...adcom.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org,
	virtualization@...ts.linux.dev,
	xen-devel@...ts.xenproject.org,
	linux-mm@...ck.org
Subject: [RFC PATCH v1 6/6] Revert "arm64/mm: Permit lazy_mmu_mode to be nested"

Commit 491344301b25 ("arm64/mm: Permit lazy_mmu_mode to be nested") made
the arm64 implementation of lazy_mmu_mode tolerant to nesting. But
subsequent commits have fixed the core code to ensure that lazy_mmu_mode
never gets nested (as originally intended). Therefore we can revert this
commit and reinstate the VM_WARN() if nesting is detected in future.

Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
 arch/arm64/include/asm/pgtable.h | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index add75dee49f5..dcf0adbeb803 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -83,21 +83,11 @@ static inline void queue_pte_barriers(void)
 #define  __HAVE_ARCH_ENTER_LAZY_MMU_MODE
 static inline void arch_enter_lazy_mmu_mode(void)
 {
-	/*
-	 * lazy_mmu_mode is not supposed to permit nesting. But in practice this
-	 * does happen with CONFIG_DEBUG_PAGEALLOC, where a page allocation
-	 * inside a lazy_mmu_mode section (such as zap_pte_range()) will change
-	 * permissions on the linear map with apply_to_page_range(), which
-	 * re-enters lazy_mmu_mode. So we tolerate nesting in our
-	 * implementation. The first call to arch_leave_lazy_mmu_mode() will
-	 * flush and clear the flag such that the remainder of the work in the
-	 * outer nest behaves as if outside of lazy mmu mode. This is safe and
-	 * keeps tracking simple.
-	 */
-
 	if (in_interrupt())
 		return;
 
+	VM_WARN_ON(test_thread_flag(TIF_LAZY_MMU));
+
 	set_thread_flag(TIF_LAZY_MMU);
 }
 
-- 
2.43.0