From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.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 17:36:59 +0000 [thread overview]
Message-ID: <c42cc00f3902673b1a964c3d098b8c3f236cf9a1.camel@intel.com> (raw)
In-Reply-To: <318407ba-ecb6-4691-8911-645fb8c20250@amazon.com>
On Fri, 2026-01-16 at 17:28 +0000, Nikita Kalyazin wrote:
> >
> > 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.
The thing is, those no_flush() helpers actually still flush if they
need to split a page. Plus if they need to clear out lazy vmalloc
aliases it could be another flush. There are probably a lot of
opportunities to reduce flushing even beyond pre-split.
Just curious... as far as performance, have you tested this on a big
multi-socket system, where that flushing will hurt more? It's something
that has always been a fear for these directmap unmapping solutions
next prev parent reply other threads:[~2026-01-16 17:37 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
2026-01-16 17:36 ` Edgecombe, Rick P [this message]
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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