From: Nikita Kalyazin <kalyazin@amazon.com>
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Subject: Re: [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct map
Date: Fri, 16 Jan 2026 17:28:06 +0000 [thread overview]
Message-ID: <318407ba-ecb6-4691-8911-645fb8c20250@amazon.com> (raw)
In-Reply-To: <bb58a21f91113ca39f8888d718d4450a5fd72808.camel@intel.com>
On 16/01/2026 15:34, Edgecombe, Rick P wrote:
> On Fri, 2026-01-16 at 15:00 +0000, Nikita Kalyazin wrote:
>>> Does this assume the folio would not have been split after it was
>>> zapped? As in, if it was zapped at 2MB granularity (no 4KB direct
>>> map split required) but then restored at 4KB (split required)? Or
>>> it gets merged somehow before this?
>>
>> AFAIK it can't be zapped at 2MB granularity as the zapping code will
>> inevitably cause splitting because guest_memfd faults occur at the
>> base page granularity as of now.
>
> Ah, right since there are no huge pages currently. Then the huge page
> series will need to keep this in mind and figure out some solution.
> Probably worth a comment on that assumption to help anyone that changes
> it.
Makes sense. I'll leave a comment.
>
> I imagine this feature is really targeted towards machines running a
> bunch of untrusted VMs, so cloud hypervisors really. In that case the
> direct map will probably be carved up pretty quick. Did you consider
> just breaking the full direct map to 4k at the start when it's in use?
That's an interesting point, I haven't thought about it from this
perspective. We should run some tests internally to see if it'd help.
This will likely change with support for huge pages coming in though.
next prev parent reply other threads:[~2026-01-16 17:28 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-14 13:45 [PATCH v9 00/13] Direct Map Removal Support for guest_memfd Kalyazin, Nikita
2026-01-14 13:45 ` [PATCH v9 01/13] set_memory: add folio_{zap,restore}_direct_map helpers Kalyazin, Nikita
2026-01-15 10:54 ` Huacai Chen
2026-01-15 11:03 ` [PATCH v9 01/13] set_memory: add folio_{zap, restore}_direct_map helpers Nikita Kalyazin
2026-01-15 12:12 ` [PATCH v9 01/13] set_memory: add folio_{zap,restore}_direct_map helpers Heiko Carstens
2026-01-15 15:25 ` [PATCH v9 01/13] set_memory: add folio_{zap, restore}_direct_map helpers Nikita Kalyazin
2026-01-15 15:55 ` [PATCH v9 01/13] set_memory: add folio_{zap,restore}_direct_map helpers Matthew Wilcox
2026-01-15 17:45 ` [PATCH v9 01/13] set_memory: add folio_{zap, restore}_direct_map helpers Nikita Kalyazin
2026-01-15 20:05 ` David Hildenbrand (Red Hat)
2026-01-15 21:07 ` [PATCH v9 01/13] set_memory: add folio_{zap,restore}_direct_map helpers Ackerley Tng
2026-01-14 13:45 ` [PATCH v9 02/13] mm/gup: drop secretmem optimization from gup_fast_folio_allowed Kalyazin, Nikita
2026-01-15 20:04 ` David Hildenbrand (Red Hat)
2026-01-15 21:40 ` Ackerley Tng
2026-01-16 14:55 ` Nikita Kalyazin
2026-01-22 0:20 ` Ackerley Tng
2026-01-14 13:45 ` [PATCH v9 03/13] mm: introduce AS_NO_DIRECT_MAP Kalyazin, Nikita
2026-01-15 21:42 ` Ackerley Tng
2026-01-14 13:45 ` [PATCH v9 04/13] KVM: guest_memfd: Add stub for kvm_arch_gmem_invalidate Kalyazin, Nikita
2026-01-15 21:47 ` Ackerley Tng
2026-01-14 13:46 ` [PATCH v9 05/13] KVM: x86: define kvm_arch_gmem_supports_no_direct_map() Kalyazin, Nikita
2026-01-15 21:48 ` Ackerley Tng
2026-01-14 13:46 ` [PATCH v9 06/13] KVM: arm64: " Kalyazin, Nikita
2026-01-14 13:46 ` [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct map Kalyazin, Nikita
2026-01-15 20:00 ` Ackerley Tng
2026-01-16 14:56 ` Nikita Kalyazin
2026-01-22 16:34 ` Ackerley Tng
2026-01-22 18:04 ` Nikita Kalyazin
2026-01-22 20:30 ` Ackerley Tng
2026-01-22 20:40 ` Nikita Kalyazin
2026-01-15 23:04 ` Edgecombe, Rick P
2026-01-16 15:02 ` Nikita Kalyazin
2026-01-16 15:35 ` Edgecombe, Rick P
2026-01-16 15:41 ` Sean Christopherson
2026-01-16 17:32 ` Nikita Kalyazin
2026-01-16 17:51 ` Edgecombe, Rick P
2026-01-16 17:30 ` Vishal Annapurve
2026-01-16 17:51 ` Edgecombe, Rick P
2026-01-22 16:44 ` Ackerley Tng
2026-01-22 17:35 ` Edgecombe, Rick P
2026-01-22 22:47 ` Ackerley Tng
2026-01-23 0:01 ` Edgecombe, Rick P
2026-01-28 0:29 ` Ackerley Tng
2026-01-16 0:00 ` Edgecombe, Rick P
2026-01-16 15:00 ` Nikita Kalyazin
2026-01-16 15:34 ` Edgecombe, Rick P
2026-01-16 17:28 ` Nikita Kalyazin [this message]
2026-01-16 17:36 ` Edgecombe, Rick P
2026-01-16 17:51 ` Nikita Kalyazin
2026-01-16 18:10 ` Edgecombe, Rick P
2026-01-16 18:16 ` Nikita Kalyazin
2026-01-22 18:37 ` Ackerley Tng
2026-01-22 18:47 ` Nikita Kalyazin
2026-01-26 16:56 ` Nikita Kalyazin
2026-01-28 0:21 ` Ackerley Tng
2026-01-14 13:46 ` [PATCH v9 08/13] KVM: selftests: load elf via bounce buffer Kalyazin, Nikita
2026-01-14 13:46 ` [PATCH v9 09/13] KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd != -1 Kalyazin, Nikita
2026-01-15 19:39 ` Ackerley Tng
2026-01-16 15:00 ` Nikita Kalyazin
2026-01-14 13:47 ` [PATCH v9 10/13] KVM: selftests: Add guest_memfd based vm_mem_backing_src_types Kalyazin, Nikita
2026-01-14 13:47 ` [PATCH v9 11/13] KVM: selftests: cover GUEST_MEMFD_FLAG_NO_DIRECT_MAP in existing selftests Kalyazin, Nikita
2026-01-14 13:47 ` [PATCH v9 12/13] KVM: selftests: stuff vm_mem_backing_src_type into vm_shape Kalyazin, Nikita
2026-01-14 13:47 ` [PATCH v9 13/13] KVM: selftests: Test guest execution from direct map removed gmem Kalyazin, Nikita
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