From: Muchun Song <muchun.song@linux.dev>
To: Dev Jain <dev.jain@arm.com>
Cc: osalvador@suse.de, akpm@linux-foundation.org, ljs@kernel.org,
david@kernel.org, liam@infradead.org, riel@surriel.com,
vbabka@kernel.org, harry@kernel.org, jannh@google.com,
lance.yang@linux.dev, kas@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, rcampbell@nvidia.com,
apopple@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com,
joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com,
gourry@gourry.net, ying.huang@linux.alibaba.com,
j-nomura@ce.jp.nec.com, nao.horiguchi@gmail.com,
ak@linux.intel.com, mel@csn.ul.ie, pfalcato@suse.de,
jpoimboe@kernel.org, dave.hansen@intel.com, tglx@kernel.org,
catalin.marinas@arm.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com,
anshuman.khandual@arm.com
Subject: Re: [PATCH v2 6/6] mm/mprotect: use huge_ptep_get() for hugetlb
Date: Thu, 2 Jul 2026 16:29:59 +0800 [thread overview]
Message-ID: <69EA5792-0152-4ACA-9BB0-1971180F40F0@linux.dev> (raw)
In-Reply-To: <555ccf16-3abf-4f82-9ebd-5df970e9de53@arm.com>
> On Jul 2, 2026, at 13:18, Dev Jain <dev.jain@arm.com> wrote:
>
>
>
> On 02/07/26 10:43 am, Dev Jain wrote:
>> prot_none_hugetlb_entry() is the hugetlb callback for the early
>> mprotect(PROT_NONE) PFN permission walk on x86.
>>
>> The callback passes the decoded PFN to pfn_modify_allowed(). For a
>> hugetlb callback, the pte pointer refers to a hugetlb entry. On
>> architectures where hugetlb entries need huge_ptep_get(), reading that
>> entry with ptep_get() can make the permission check use the wrong PFN.
>>
>> Use huge_ptep_get() before decoding the hugetlb PFN.
>>
>> Currently there is no path which can trigger a bug: huge_ptep_get() is a
>> simple ptep_get() for x86, and the prot_none walk occurs only for x86.
>>
>> So no need to backport - use the correct helper anyways.
>>
>> Fixes: 42e4089c7890 ("x86/speculation/l1tf: Disallow non privileged high MMIO PROT_NONE mappings")
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>
> @Muchun, I did not do the change you suggested: if we do #ifdef around
> the hugetlb callback, then for CONFIG_HUGETLB_PAGE=n, prot_none_hugetlb_entry()
> is defined but not used, giving compile error.
>
Got it. Thanks for your explanation.
next prev parent reply other threads:[~2026-07-02 8:31 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-02 5:13 [PATCH v2 0/6] Fix incorrect access of hugetlb pte entries Dev Jain
2026-07-02 5:13 ` [PATCH v2 1/6] arm64: make huge_ptep_get handled unaligned addresses Dev Jain
2026-07-02 15:28 ` David Hildenbrand (Arm)
2026-07-02 5:13 ` [PATCH v2 2/6] mm/rmap: use huge_ptep_get() in try_to_unmap_one() Dev Jain
2026-07-02 8:47 ` Muchun Song
2026-07-02 9:08 ` Dev Jain
2026-07-02 9:35 ` Muchun Song
2026-07-02 15:30 ` David Hildenbrand (Arm)
2026-07-02 15:32 ` David Hildenbrand (Arm)
2026-07-02 5:13 ` [PATCH v2 3/6] mm/rmap: use huge_ptep_get() in try_to_migrate_one() Dev Jain
2026-07-02 15:34 ` David Hildenbrand (Arm)
2026-07-02 5:13 ` [PATCH v2 4/6] mm/migrate: use huge_ptep_get() in remove_migration_pte() Dev Jain
2026-07-02 15:44 ` David Hildenbrand (Arm)
2026-07-02 5:13 ` [PATCH v2 5/6] mm/page_vma_mapped: use huge_ptep_get() for hugetlb Dev Jain
2026-07-02 8:33 ` Muchun Song
2026-07-02 15:44 ` David Hildenbrand (Arm)
2026-07-02 5:13 ` [PATCH v2 6/6] mm/mprotect: " Dev Jain
2026-07-02 5:18 ` Dev Jain
2026-07-02 8:29 ` Muchun Song [this message]
2026-07-02 8:30 ` Muchun Song
2026-07-02 15:47 ` David Hildenbrand (Arm)
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