linux-kernel - [v3 PATCH 0/2] KVM: guest_memfd: use write for population

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Message-ID: <20250303130838.28812-1-kalyazin@amazon.com>
Date: Mon, 3 Mar 2025 13:08:36 +0000
From: Nikita Kalyazin <kalyazin@...zon.com>
To: <pbonzini@...hat.com>, <shuah@...nel.org>
CC: <kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <michael.day@....com>, <david@...hat.com>,
	<quic_eberman@...cinc.com>, <jthoughton@...gle.com>, <brijesh.singh@....com>,
	<michael.roth@....com>, <graf@...zon.de>, <jgowans@...zon.com>,
	<roypat@...zon.co.uk>, <derekmn@...zon.com>, <nsaenz@...zon.es>,
	<xmarcalx@...zon.com>, <kalyazin@...zon.com>
Subject: [v3 PATCH 0/2] KVM: guest_memfd: use write for population

This series is rebased on top of Fuad's v4 for shared mapping of
guest_memfd [1].

Change since v2 [2]:
 - David/Mike D: Only compile support for the write syscall if
   CONFIG_KVM_GMEM_SHARED_MEM introduced in [1] is enabled.

In non-CoCo use cases where the host can access guest memory,
guest_memfd can be allocated and populated via the write syscall.  Even
though the same can also be achieved via userspace mapping and memcpy
from userspace, write provides a more performant option because it 1)
avoids double initialisation as the kernel does not need to zero pages
and 2) does not require setting up page tables.

Nikita

[1] https://lore.kernel.org/kvm/20250218172500.807733-4-tabba@google.com/T/
[2] https://lore.kernel.org/kvm/20241129123929.64790-1-kalyazin@amazon.com/T/

Nikita Kalyazin (2):
  KVM: guest_memfd: add generic population via write
  KVM: selftests: update guest_memfd write tests

 .../testing/selftests/kvm/guest_memfd_test.c  | 85 +++++++++++++++--
 virt/kvm/guest_memfd.c                        | 94 ++++++++++++++++++-
 2 files changed, 170 insertions(+), 9 deletions(-)


base-commit: 005f6404708d430abab7fab9b422d0daf6e0c2fe
-- 
2.47.1