From: Mark Brown <broonie@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Deepak Gupta <debug@rivosinc.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Will Deacon <will@kernel.org>, Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-mm@kvack.org
Subject: Re: [PATCH 5/5] mm: Do not map the shadow stack as THP
Date: Wed, 25 Feb 2026 16:10:18 +0000 [thread overview]
Message-ID: <a44708a8-ec02-41fa-b870-a649f13072f4@sirena.org.uk> (raw)
In-Reply-To: <aZ8aeHpn_KElP2jm@arm.com>
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On Wed, Feb 25, 2026 at 03:51:20PM +0000, Catalin Marinas wrote:
> On Wed, Feb 25, 2026 at 01:02:36PM +0000, Mark Brown wrote:
> > The create THP and immediately splitting it pattern is very clear when
> > checking the mm behaviour on new GCSs, this should help performance.
> If the first access is a write, the kernel allocates a THP from the
> start without subsequent splitting. Also since 6.13 (commit 1ced09e0331f
Ah, it seems this has been optimised since I looked in detail - it was
something I was aware of as needing some work.
> "mm: allocate THP on hugezeropage wp-fault"), we go for another THP on
> write. It's still wasting memory and time to zero the full 2MB when
> it's highly unlikely we'd ever use that much for a shadow stack.
Yeah, for a shadow stack I'd be surprised if it wasn't cheaper to split
than do all that.
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next prev parent reply other threads:[~2026-02-25 16:10 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-24 17:57 [PATCH 0/5] mm: arch/shstk: Common shadow stack mapping helper and VM_NOHUGEPAGE Catalin Marinas
2026-02-24 17:57 ` [PATCH 1/5] mm: Introduce vm_mmap_shadow_stack() as a helper for VM_SHADOW_STACK mappings Catalin Marinas
2026-02-24 19:47 ` Edgecombe, Rick P
2026-02-25 12:25 ` Mark Brown
2026-02-25 13:32 ` David Hildenbrand (Arm)
2026-02-24 17:57 ` [PATCH 2/5] arm64: gcs: Use the new common vm_mmap_shadow_stack() helper Catalin Marinas
2026-02-25 13:32 ` David Hildenbrand (Arm)
2026-02-25 13:41 ` Mark Brown
2026-02-24 17:57 ` [PATCH 3/5] riscv: shstk: " Catalin Marinas
2026-02-25 13:33 ` David Hildenbrand (Arm)
2026-02-24 17:57 ` [PATCH 4/5] x86: " Catalin Marinas
2026-02-24 19:47 ` Edgecombe, Rick P
2026-02-25 8:12 ` Catalin Marinas
2026-02-25 13:33 ` David Hildenbrand (Arm)
2026-02-24 17:57 ` [PATCH 5/5] mm: Do not map the shadow stack as THP Catalin Marinas
2026-02-25 13:02 ` Mark Brown
2026-02-25 15:51 ` Catalin Marinas
2026-02-25 16:10 ` Mark Brown [this message]
2026-02-25 13:34 ` David Hildenbrand (Arm)
2026-02-25 0:06 ` [PATCH 0/5] mm: arch/shstk: Common shadow stack mapping helper and VM_NOHUGEPAGE Deepak Gupta
2026-02-25 8:08 ` Catalin Marinas
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