From patchwork Mon Nov 7 21:56:30 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oliver Upton X-Patchwork-Id: 13035334 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 6CAAAC433FE for ; Mon, 7 Nov 2022 21:57:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232277AbiKGV5d (ORCPT ); Mon, 7 Nov 2022 16:57:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232112AbiKGV5b (ORCPT ); Mon, 7 Nov 2022 16:57:31 -0500 Received: from out0.migadu.com (out0.migadu.com [94.23.1.103]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 50C0327DE5 for ; Mon, 7 Nov 2022 13:57:29 -0800 (PST) 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=1667858248; 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=K8pNk8hWUq4Y0+/KZMKfTCv81iZIAJaiRKw2wKJYvsE=; b=N6Xlo3L3F26NzaElzf6V6LstKEForCmo6VqnF13KdaUb2R7f+OkCQPZbaqB5WxzuOamgci halbKIs/tFt23TR+R95UMcp5PPaCj4Rchie+kdGC1y5iyFy8+6FtR2TcwJvxeEUuvmTN8R +/Wb3+jbrSsXuPw76AUlmTDIBKJ3OKw= 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 v5 00/14] KVM: arm64: Parallel stage-2 fault handling Date: Mon, 7 Nov 2022 21:56:30 +0000 Message-Id: <20221107215644.1895162-1-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 5-7 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. Patch 8 sprinkles in RCU to the page table walkers, punting the teardown of removed tables to an RCU callback. Patches 9-13 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 14 flips the switch on all the new code and starts grabbing the read side of the MMU lock for stage 2 faults. Applies to 6.1-rc3. Tested with KVM selftests, kvm-unit-tests, and live migrating a 24 vCPU, 96GB VM that was running a Debian install. Confirmed all stage-2 table memory was freed by checking the SecPageTables stat in meminfo. Branch available at: https://github.com/oupton/linux kvm-arm64/parallel_mmu 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 | 6.1-rc3 | 6.1-rc3 + 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 | 6.1-rc3 | 6.1-rc3 + 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 | +-------+----------+-------------------+ v4 -> v5: - Fix an obvious leak of table memory (Ricardo) v3 -> v4: - Fix some type conversion misses caught by sparse (test robot) - Squash RCU locking and RCU callback patches together into one (Sean) - Commit message nits (Sean) - Take a pointer to kvm_s2_mmu in stage2_try_break_pte(), in anticipation of eager page splitting (Ricardo) v3: https://lore.kernel.org/kvmarm/20221027221752.1683510-1-oliver.upton@linux.dev/ v4: https://lore.kernel.org/kvmarm/20221103091140.1040433-1-oliver.upton@linux.dev/ Oliver Upton (14): 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: Use an opaque type for pteps KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make KVM: arm64: Protect stage-2 traversal with RCU 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 | 92 +++- arch/arm64/kvm/hyp/nvhe/mem_protect.c | 21 +- arch/arm64/kvm/hyp/nvhe/setup.c | 22 +- arch/arm64/kvm/hyp/pgtable.c | 628 ++++++++++++++------------ arch/arm64/kvm/mmu.c | 53 ++- 5 files changed, 466 insertions(+), 350 deletions(-) base-commit: 30a0b95b1335e12efef89dd78518ed3e4a71a763