From: "Brendan Jackman" <brendan.jackman@linux.dev>
To: "Marc Zyngier" <maz@kernel.org>,
"Kalyazin, Nikita" <kalyazin@amazon.co.uk>
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Subject: Re: [PATCH v12 09/16] KVM: arm64: define kvm_arch_gmem_supports_no_direct_map()
Date: Fri, 26 Jun 2026 14:45:45 +0000 [thread overview]
Message-ID: <DJJ28Z81JTQI.1SI0CNIP7W1JQ@linux.dev> (raw)
In-Reply-To: <86fr4o1ceu.wl-maz@kernel.org>
On Tue Apr 21, 2026 at 4:55 PM UTC, Marc Zyngier wrote:
> On Fri, 10 Apr 2026 16:19:24 +0100,
> "Kalyazin, Nikita" <kalyazin@amazon.co.uk> wrote:
>>
>> From: Patrick Roy <patrick.roy@linux.dev>
>>
>> Support for GUEST_MEMFD_FLAG_NO_DIRECT_MAP on arm64 depends on 1) direct
>> map manipulations at 4k granularity being possible, and 2) FEAT_S2FWB.
>>
>> 1) is met whenever the direct map is set up at 4k granularity (e.g. not
>> with huge/gigantic pages) at boottime, as due to ARM's
>> break-before-make semantics, breaking huge mappings into 4k mappings in
>> the direct map is not possible (BBM would require temporary invalidation
>> of the entire huge mapping, even if only a 4k subrange should be zapped,
>> which will probably crash the kernel). However, the current default for
>> rodata_full is true, which forces a 4k direct map.
>
> Where is this 4kB requirement enforced? Or is it that you means
> "PAGE_SIZE"?
Yeah I believe this means PAGE_SIZE and that it's effectively enforced
by checking can_set_direct_map() in
kvm_arch_gmem_supports_no_direct_map().
next prev parent reply other threads:[~2026-06-26 14:45 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-10 15:17 [PATCH v12 00/16] Direct Map Removal Support for guest_memfd Kalyazin, Nikita
2026-04-10 15:17 ` [PATCH v12 01/16] set_memory: set_direct_map_* to take address Kalyazin, Nikita
2026-04-21 14:43 ` Lorenzo Stoakes
2026-06-26 14:38 ` Brendan Jackman
2026-06-26 14:58 ` David Hildenbrand (Arm)
2026-06-26 15:08 ` Brendan Jackman
2026-06-26 15:04 ` Brendan Jackman
2026-06-26 15:28 ` Mike Rapoport
2026-04-10 15:18 ` [PATCH v12 02/16] set_memory: add folio_{zap,restore}_direct_map helpers Kalyazin, Nikita
2026-04-10 15:18 ` [PATCH v12 03/16] mm/secretmem: make use of folio_{zap,restore}_direct_map Kalyazin, Nikita
2026-04-10 15:18 ` [PATCH v12 04/16] mm/gup: drop secretmem optimization from gup_fast_folio_allowed Kalyazin, Nikita
2026-04-10 15:18 ` [PATCH v12 05/16] mm/gup: drop local variable in gup_fast_folio_allowed Kalyazin, Nikita
2026-04-10 15:18 ` [PATCH v12 06/16] mm: introduce AS_NO_DIRECT_MAP Kalyazin, Nikita
2026-04-10 15:19 ` [PATCH v12 07/16] KVM: guest_memfd: Add stub for kvm_arch_gmem_invalidate Kalyazin, Nikita
2026-04-10 15:19 ` [PATCH v12 08/16] KVM: x86: define kvm_arch_gmem_supports_no_direct_map() Kalyazin, Nikita
2026-04-10 15:19 ` [PATCH v12 09/16] KVM: arm64: " Kalyazin, Nikita
2026-04-21 16:55 ` Marc Zyngier
2026-06-26 14:45 ` Brendan Jackman [this message]
2026-04-10 15:19 ` [PATCH v12 10/16] KVM: guest_memfd: Add flag to remove from direct map Kalyazin, Nikita
2026-04-21 16:31 ` Sean Christopherson
2026-04-21 17:08 ` Frank van der Linden
2026-05-08 8:18 ` Takahiro Itazuri
2026-05-14 16:45 ` Ackerley Tng
2026-04-10 15:19 ` [PATCH v12 11/16] KVM: selftests: load elf via bounce buffer Kalyazin, Nikita
2026-04-10 15:19 ` [PATCH v12 12/16] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd != -1 Kalyazin, Nikita
2026-04-10 15:20 ` [PATCH v12 13/16] KVM: selftests: Add guest_memfd based vm_mem_backing_src_types Kalyazin, Nikita
2026-06-26 14:22 ` Brendan Jackman
2026-04-10 15:20 ` [PATCH v12 14/16] KVM: selftests: cover GUEST_MEMFD_FLAG_NO_DIRECT_MAP in existing selftests Kalyazin, Nikita
2026-04-10 15:20 ` [PATCH v12 15/16] KVM: selftests: stuff vm_mem_backing_src_type into vm_shape Kalyazin, Nikita
2026-04-10 15:20 ` [PATCH v12 16/16] KVM: selftests: Test guest execution from direct map removed gmem Kalyazin, Nikita
2026-04-21 13:40 ` [PATCH v12 00/16] Direct Map Removal Support for guest_memfd Lorenzo Stoakes
2026-04-21 16:36 ` Sean Christopherson
2026-05-06 8:07 ` Takahiro Itazuri
2026-05-26 16:27 ` Lorenzo Stoakes
2026-06-26 15:28 ` Brendan Jackman
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