From patchwork Fri Oct 7 23:28:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oliver Upton X-Patchwork-Id: 13001517 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C25CCC433F5 for ; Fri, 7 Oct 2022 23:28:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229611AbiJGX26 (ORCPT ); Fri, 7 Oct 2022 19:28:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36548 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229525AbiJGX25 (ORCPT ); Fri, 7 Oct 2022 19:28:57 -0400 Received: from out0.migadu.com (out0.migadu.com [IPv6:2001:41d0:2:267::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C69BE3ED70 for ; Fri, 7 Oct 2022 16:28:54 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1665185333; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=IqVEPYz9+Fk1DulCf4KAHqaS32S3zy4XGu1z8gZcQ94=; b=pYQp11XQNriZ+v/ARcUhe8A+GQ7yNuy9LrtksDb6vpIQTg1hwnvAxhc7q08mU+Y3BzX8ep B7OPKEmXmAzzaf5ykrO5MTYT+f0JieJM8+b+ErEYI19fDngXuTl6cgefHXovVKeL88rMKt i78ucXL/xIeCh/gWu/NZitqkjuewKKE= From: Oliver Upton To: Marc Zyngier , James Morse , Alexandru Elisei Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Reiji Watanabe , Ricardo Koller , David Matlack , Quentin Perret , Ben Gardon , Gavin Shan , Peter Xu , Will Deacon , Sean Christopherson , kvmarm@lists.linux.dev, Oliver Upton Subject: [PATCH v2 00/15] KVM: arm64: Parallel stage-2 fault handling Date: Fri, 7 Oct 2022 23:28:03 +0000 Message-Id: <20221007232818.459650-1-oliver.upton@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Presently KVM only takes a read lock for stage 2 faults if it believes the fault can be fixed by relaxing permissions on a PTE (write unprotect for dirty logging). Otherwise, stage 2 faults grab the write lock, which predictably can pile up all the vCPUs in a sufficiently large VM. Like the TDP MMU for x86, this series loosens the locking around manipulations of the stage 2 page tables to allow parallel faults. RCU and atomics are exploited to safely build/destroy the stage 2 page tables in light of multiple software observers. Patches 1-4 clean up the context associated with a page table walk / PTE visit. This is helpful for: - Extending the context passed through for a visit - Building page table walkers that operate outside of a kvm_pgtable context (e.g. RCU callback) Patches 5-6 clean up the stage-2 map walkers by calling a helper to tear down removed tables. There is a small improvement here in that a broken PTE is replaced more quickly, as page table teardown happens afterwards. Patches 7-9 sprinkle in RCU to the page table walkers, punting the teardown of removed tables to an RCU callback. Patches 10-14 implement the meat of this series, extending the 'break-before-make' sequence with atomics to realize locking on PTEs. Effectively a cmpxchg() is used to 'break' a PTE, thereby serializing changes to a given PTE. Finally, patch 15 flips the switch on all the new code and starts grabbing the read side of the MMU lock for stage 2 faults. Applies to kvmarm-6.1. Tested with KVM selftests, kvm-unit-tests, and Google's internal VMM (Vanadium). Also tested with lockdep enabled and saw no puke for RCU. Planning on following up testing migration with QEMU. Got frustrated with my cross-building environment and I wanted to get the patches out before the weekend :) benchmarked with dirty_log_perf_test, scaling from 1 to 48 vCPUs with 4GB of memory per vCPU backed by THP. ./dirty_log_perf_test -s anonymous_thp -m 2 -b 4G -v ${NR_VCPUS} Time to dirty memory: +-------+---------+------------------+ | vCPUs | kvmarm | kvmarm + series | +-------+---------+------------------+ | 1 | 0.87s | 0.93s | | 2 | 1.11s | 1.16s | | 4 | 2.39s | 1.27s | | 8 | 5.01s | 1.39s | | 16 | 8.89s | 2.07s | | 32 | 19.90s | 4.45s | | 48 | 32.10s | 6.23s | +-------+---------+------------------+ It is also worth mentioning that the time to populate memory has improved: +-------+---------+------------------+ | vCPUs | kvmarm | kvmarm + series | +-------+---------+------------------+ | 1 | 0.21s | 0.17s | | 2 | 0.26s | 0.23s | | 4 | 0.39s | 0.31s | | 8 | 0.68s | 0.39s | | 16 | 1.26s | 0.53s | | 32 | 2.51s | 1.04s | | 48 | 3.94s | 1.55s | +-------+---------+------------------+ v1 -> v2: - It builds! :-) - Roll all of the context associated with PTE visit into a stack-allocated structure - Clean up the oddball handling of PTE values, avoiding a UAF along the way (Quentin) - Leave the re-reading of the PTE after WALK_LEAF in place instead of attempting to return the installed PTE value (David) - Mention why RCU is stubbed out for hyp page table walkers (David) - Ensure that all reads of page table memory pass through an RCU-protected pointer. The lifetime of the dereference is contained within __kvm_pgtable_visit() (David). - Ensure that no user of stage2_map_walker() passes TABLE_POST (David) - Unwire the page table walkers from relying on struct kvm_pgtable, simplifying the passed context to RCU callbacks. - Key rcu_dereference() off of a page table flag indicating a shared walk. This is clear when either (1) the write lock is held or (2) called from an RCU callback. v1: https://lore.kernel.org/kvmarm/20220830194132.962932-1-oliver.upton@linux.dev/ Oliver Upton (15): KVM: arm64: Combine visitor arguments into a context structure KVM: arm64: Stash observed pte value in visitor context KVM: arm64: Pass mm_ops through the visitor context KVM: arm64: Don't pass kvm_pgtable through kvm_pgtable_walk_data KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make KVM: arm64: Use an opaque type for pteps KVM: arm64: Protect stage-2 traversal with RCU KVM: arm64: Free removed stage-2 tables in RCU callback KVM: arm64: Atomically update stage 2 leaf attributes in parallel walks KVM: arm64: Split init and set for table PTE KVM: arm64: Make block->table PTE changes parallel-aware KVM: arm64: Make leaf->leaf PTE changes parallel-aware KVM: arm64: Make table->block changes parallel-aware KVM: arm64: Handle stage-2 faults in parallel arch/arm64/include/asm/kvm_pgtable.h | 85 +++- arch/arm64/kvm/hyp/nvhe/mem_protect.c | 21 +- arch/arm64/kvm/hyp/nvhe/setup.c | 22 +- arch/arm64/kvm/hyp/pgtable.c | 624 ++++++++++++++------------ arch/arm64/kvm/mmu.c | 51 ++- 5 files changed, 456 insertions(+), 347 deletions(-) base-commit: b302ca52ba8235ff0e18c0fa1fa92b51784aef6a