From: Yang Shi <yang@os•amperecomputing.com>
To: Jann Horn <jannh@google•com>, Dave Hansen <dave.hansen@intel•com>
Cc: Xueyuan chen <xueyuan.chen21@gmail•com>,
akpm@linux-foundation•org, linux-mm@kvack•org,
linux-kernel@vger•kernel.org,
linux-arm-kernel@lists•infradead.org, x86@kernel•org,
catalin.marinas@arm•com, will@kernel•org, tglx@kernel•org,
mingo@redhat•com, bp@alien8•de, dave.hansen@linux•intel.com,
hpa@zytor•com, david@kernel•org, ljs@kernel•org, ziy@nvidia•com,
baolin.wang@linux•alibaba.com, ryan.roberts@arm•com,
dev.jain@arm•com, lance.yang@linux•dev
Subject: Re: [RFC PATCH 1/3] mm: make persistent huge zero folio read-only
Date: Thu, 28 May 2026 11:43:40 -0700 [thread overview]
Message-ID: <c0f9a811-0286-4e1c-8790-8e31d95e5819@os.amperecomputing.com> (raw)
In-Reply-To: <CAG48ez2qj+QkLZvvi+6S78_v4Zk2eZBnBx6TozwgG4payOqPLg@mail.gmail.com>
On 5/27/26 9:20 AM, Jann Horn wrote:
> On Wed, May 27, 2026 at 5:55 PM Dave Hansen <dave.hansen@intel•com> wrote:
>> On 5/26/26 20:56, Xueyuan chen wrote:
>>> +config READONLY_HUGE_ZERO_FOLIO
>>> + bool "Map the huge zero folio read-only in the direct map"
>>> + depends on PERSISTENT_HUGE_ZERO_FOLIO
>>> + depends on ARCH_HAS_READONLY_HUGE_ZERO_FOLIO
>>> + help
>>> + The persistent huge zero folio is shared globally, and nothing
>>> + should ever change its contents after initialization.
>>> +
>>> + When supported, mark the folio read-only in the direct map so such
>>> + writes trigger a fault instead of silently corrupting the zero contents.
>>> +
>>> + If the permission change is not supported, the kernel keeps using
>>> + the writable persistent huge zero folio.
>> I vote for no Kconfig options here. Why? This adds "security" with
>> _basically_ no extra runtime cost. The runtime cost is, what, usually
>> one kernel TLB invalidation during boot?
> Plus potentially a bit more TLB pressure from losing a huge PUD in the
> linear map, IDK how much we care about that.
This shouldn't be a big issue on ARM64. The most ARM64 machines have
linear mapping mapped with PTE if rodata is on. Some machines with
BBML2_NOABORT support have linear mapping mapped with PUD/PMD, but those
machines typically have large memory, having 512 PMDs instead of 1 PUD
shouldn't be a noticeable issue IMHO.
Thanks,
Yang
next prev parent reply other threads:[~2026-05-28 18:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-27 3:56 [RFC PATCH 0/3] make persistent huge zero folio read-only Xueyuan chen
2026-05-27 3:56 ` [RFC PATCH 1/3] mm: " Xueyuan chen
2026-05-27 13:32 ` Dev Jain
2026-05-27 23:03 ` Xueyuan Chen
2026-05-27 15:55 ` Dave Hansen
2026-05-27 16:20 ` Jann Horn
2026-05-28 18:43 ` Yang Shi [this message]
2026-05-29 3:09 ` Lance Yang
2026-06-01 13:49 ` David Hildenbrand (Arm)
2026-06-01 15:43 ` Lance Yang
2026-06-01 15:46 ` David Hildenbrand (Arm)
2026-05-27 3:56 ` [RFC PATCH 2/3] arm64/mm: make huge zero folio read-only in linear map Xueyuan chen
2026-05-27 3:56 ` [RFC PATCH 3/3] x86/mm: make huge zero folio read-only in direct map Xueyuan chen
2026-05-27 15:58 ` [RFC PATCH 0/3] make persistent huge zero folio read-only Dave Hansen
2026-05-30 7:46 ` Lance Yang
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