From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 98D1C3A1C9; Tue, 25 Aug 2026 16:01:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787673674; cv=none; b=I1nCyaNfSFVqczc+wlyrv8XacZrmTay2PfDnSm6pHcHBnlabhaV8YVe0hEkUmWc1j3/7K9LGb2aXLzho+SZhop64QLHq6f8s+gUda4i+/0ZeClSzvAJeepOgX4bao94dVjdKabBxe08frnyzeEWrQPy2ml92hSpJnDUYdoJZ7gU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787673674; c=relaxed/simple; bh=shQu2ja8FKYpxwmft95PQDnR4lutE8cOna4MUXeJkaA=; h=From:Subject:Date:Message-Id:MIME-Version:Content-Type:To:Cc; b=t6s738wO3q0xXWz2/+km2yNlJv8ELbyJV/86SVFB6J+FjCJ0DzyVt+brGAuW0DeV0aDG5i9iyGAmYPQs4VAHpcc9JGZg+BorJbi0aU68fmwWtkgacwPj2LHk1uNKLyCiCZlesJTGLulnExGA16uamusQ1Ek46G1rhW5EzsGxJhI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ar2uwwun; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ar2uwwun" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD5681F000E9; Tue, 25 Aug 2026 16:01:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787673673; bh=0UWZ5amjuDuz5NxB+UBQVKLusjTJjNvSXdFmO8uoJLU=; h=From:Subject:Date:To:Cc; b=Ar2uwwun9E+GAnctXWPBo12NcRgbRk8j7SLZV8gbV1A3osQAyzyUx4CPw/tOz/kPp XEXxZ4DgeolskSEIGxUXXSP8OkioSdv3k4urTIPJsg59Vna8moQ/DmcAcq22P6ALH1 KyA5ngiOVDGxFU6oybyDKr74CTlBbS7fsl0bThU0iogWxKi42cHP02vWV0QsTwXb6X 5TEIf6o6guYYaPPpSt30Ep96YTrqC57eBz7n4bIB7D4u2p8qdzlmIVTinMoSZ0mXxu pY97bxnxk5iczGyJPPLO2T1NMv/pGx5UYLv/HVpnMdFj0q7ZzSLBC+q6TtjG3c0dBW DGx77mzSKlyYw== From: "Lorenzo Stoakes (ARM)" Subject: [PATCH 0/8] KVM: arm64: Add KVM_PRE_FAULT_MEMORY support Date: Tue, 25 Aug 2026 17:00:34 +0100 Message-Id: <20260825-kvm-arm-prefault-v1-0-befe8947702e@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAAAAAAAC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDIzMDC0NT3eyyXN3EolzdgqLUtMTSnBJdy6QkE0PDJDMLS/MUJaA2kERmBdj I6NjaWgB0ns9XYgAAAA== X-Change-ID: 20260815-kvm-arm-prefault-9bb411b6897d To: Catalin Marinas , Will Deacon , Marc Zyngier , Oliver Upton , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Paolo Bonzini , Jonathan Corbet Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Jack Thomson , Jack Thomson , Alexandru Elisei , Vincent Donnefort , "Aneesh Kumar K.V" , Sean Christopherson , Claudio Imbrenda , Leo Soares Passos , "Lorenzo Stoakes (ARM)" X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=5144; i=ljs@kernel.org; h=from:subject:message-id; bh=shQu2ja8FKYpxwmft95PQDnR4lutE8cOna4MUXeJkaA=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLJ69zgpbqu+wXsyfM3+Pc//BZRP4Cm8mpD614CD7UqQZ u+nDgnfjlIWBjEuBlkxRZbnX8T3B4mEzeu84O8GM4eVCWQIAxenAExEn5fhr4DtqQdGhxvvP3QR 2MYn/Dtv1t6g6QIb81smzJjoLfGX0ZKR4YGBQYXBhTUqu1RXv7r2oPr9grcsFpPrw273vjvVtdV 5CQcA X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 This series implements the KVM stage 2 page table pre-faulting feature for arm64. == Foundations == The series begins by establishing required foundations: 1. Updating kvm_s2_fault_desc to independently store the exception syndrome register (ESR) value, and updating all code paths to use this value exclusively. This is needed so we can later generate a synthetic fault to perform the pre-faulting - we need to be sure the code doesn't grab an incorrect ESR from elsewhere. 2. Updating kvm_s2_fault_desc to independently store the kvm_s2_mmu and updating all code paths to use this value exclusively. Similarly this is needed so we can generate a synthetic fault against the canonical stage 2 MMU (it would make no sense for it to touch nested shadow page tables) - we need to be sure that the code doesn't grab an incorrect MMU from elsewhere. 3. Updating the abort paths which consume kvm_s2_fault_desc to also return a kvm_s2_fault_result data structure. To perform pre-faulting the code must know the granule size of what was just walked. So the abort paths have to tell us what that was. 4. Pass walk flags to kvm_pgtable_get_leaf() to permit walking page tables under the MMU read lock. This is Jack's patch, verbatim, which allows the use of the KVM_PGTABLE_WALK_SHARED flag to walk page tables under the MMU read lock. Pre-faulting requires it to be able to work in parallel as specified by the API. The read lock precludes page tables being torn down behind our back. == Implementation == Pre-faulting is implemented in kvm_arch_vcpu_pre_fault_memory() whose job is to pre-fault the stage 2 page tables which map a specific GPA (which, for arm64, is the guest's IPA). This function is called by kvm_vcpu_pre_fault_memory() for each GPA in the range, which itself is ultimately invoked by userland via the KVM_PRE_FAULT_MEMORY ioctl. The implementation is simple - try to walk to the stage 2 page table mapping the GPA - if unmapped, fault it in through a synthetic page fault. pKVM is not supported regardless of whether the VM is protected or not. This is because pKVM instantiates vCPUs upon run, but pre-faulting is typically performed before a vCPU is run. It would be confusing and inconsistent to error out on non-running vCPUs but to pre-fault running ones. Jack's original test suite is also included in the series. == Credits == This series is based, with gratitude, on Jack Thomson's series and their respins (links provided below) as well as the feedback he received. The series includes Jack's v5 "KVM: arm64: Pass walk flags to kvm_pgtable_get_leaf()" patch verbatim, and all three of his test patches, two of which required minor fixups. Link: https://patch.msgid.link/20260612162354.73378-1-jackabt.amazon@gmail.com/ Link: https://patch.msgid.link/20260113152643.18858-1-jackabt.amazon@gmail.com/ Link: https://patch.msgid.link/20251119154910.97716-1-jackabt.amazon@gmail.com/ Link: https://patch.msgid.link/20251013151502.6679-1-jackabt.amazon@gmail.com/ Link: https://patch.msgid.link/20250911134648.58945-1-jackabt.amazon@gmail.com/ == Reviewer Notes == I synced with maintainers on this who asked me to take a look, as there hadn't been progress on the series for some time. Am happy to rebase again after -rc1. Signed-off-by: Lorenzo Stoakes (ARM) --- Jack Thomson (4): KVM: arm64: Pass walk flags to kvm_pgtable_get_leaf() KVM: selftests: Enable pre_fault_memory_test for arm64 KVM: selftests: Add option for different backing in pre-fault tests KVM: selftests: Add nested pre-fault test for arm64 Lorenzo Stoakes (ARM) (4): KVM: arm64: Propagate and use esr in s2fd when handling guest aborts KVM: arm64: Propagate and use mmu in s2fd when handling guest aborts KVM: arm64: Propagate and use kvm_s2_fault_result on S2 fault KVM: arm64: Implement KVM_PRE_FAULT_MEMORY Documentation/virt/kvm/api.rst | 17 +- arch/arm64/include/asm/esr.h | 129 +++++--- arch/arm64/include/asm/kvm_emulate.h | 52 +--- arch/arm64/include/asm/kvm_pgtable.h | 5 +- arch/arm64/include/asm/kvm_pkvm.h | 2 +- arch/arm64/kvm/Kconfig | 1 + arch/arm64/kvm/arm.c | 1 + arch/arm64/kvm/hyp/nvhe/mem_protect.c | 10 +- arch/arm64/kvm/hyp/pgtable.c | 5 +- arch/arm64/kvm/mmu.c | 324 +++++++++++++++++---- arch/arm64/kvm/nested.c | 2 +- tools/testing/selftests/kvm/Makefile.kvm | 2 + .../selftests/kvm/arm64/nv_pre_fault_memory_test.c | 206 +++++++++++++ .../testing/selftests/kvm/pre_fault_memory_test.c | 152 ++++++++-- 14 files changed, 736 insertions(+), 172 deletions(-) --- base-commit: aa8e5dc6a7a2a1141ab40706a51010adcd0e57d2 change-id: 20260815-kvm-arm-prefault-9bb411b6897d Best regards, -- Lorenzo Stoakes (ARM)