From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A428EC433DB for ; Fri, 26 Mar 2021 02:21:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8262861A3E for ; Fri, 26 Mar 2021 02:21:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231281AbhCZCVT (ORCPT ); Thu, 25 Mar 2021 22:21:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231305AbhCZCUq (ORCPT ); Thu, 25 Mar 2021 22:20:46 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0AF8C061763 for ; Thu, 25 Mar 2021 19:20:45 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id g9so8288434ybc.19 for ; Thu, 25 Mar 2021 19:20:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=TaRsW9hCT9gEJ/YVzW7kB9YFbRu5cnB3H0FViU1bRhk=; b=kBPgGMYl4blfSBIqQ5FKhwNHBKbvitDKr+WZYdt/8IhMnlfsrTKNXxhUeD4Dfv4OdK Qp85biDD6s+K+U5KksvGPm1ktvKtYdF7mnE9MrHxMeaVxGrZG5ap40dtbvhTh6LLvRmq EVe4q3actfo6eycSfr6QO9c/QHHJUOWKxLFg2JRrhbugVxZPDZF4Tws0K8Q0zTr01x17 AhbFvngDP583OBSyiGm1/Mz3bjEOz7lQ/Yjo2wW5h41dxHGv5x1vrgqkeUC6D0RE05dK 3WjGfoR4fP8tf2U8RHVaSt/5IZ2QjRAtja0LwszjEpZxXU5VWS0iy7Sr4MaEgtMnRZgZ ZNJQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=TaRsW9hCT9gEJ/YVzW7kB9YFbRu5cnB3H0FViU1bRhk=; b=QS7k5bMjBkgHI7FQuPxXHS/sVBYB6wco94msYF4NrT0hVNpeC+Sc/Kv2qhcJgQPOF+ iISrxe7/So5OCyvXVNWuWqFhhXk2DO9Sk0PY0ITUqiPmoVeXb58M0IalRXpotTWus6Om Xu4xWk6loIgvL+Ou+GjrpxuL8vczZdgsN2q9FXt+AitIo8YlWNplickLawvncBa+ifSu G6o0Krz3+BiHjdkGeg8v/oOKZlEviOdVQtsvycIqAEUlp5+cgIMVMSjsf0vrm2vYdaVT ZAnQinY2Pikx00/SXJrUJA80n2g3GzlVpyiqbfWhCpXMgkR/9JWe8Jw4FjXA4JnL/CIL S9tw== X-Gm-Message-State: AOAM533OUchYa412CG9ytjAfz03bPxt082/c008WMgwfm4S8ZS5jmt9W Cmz6LNByUv2dBgB1+e11kl78S7djBLM= X-Google-Smtp-Source: ABdhPJy2kLsKpNboktKYvRYtclaI6TLQhJXYHuQbVsBNzQbrVXujQcH971ASv0KdE05FkcrHFObwQrNjrD8= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:f:10:b1bb:fab2:7ef5:fc7d]) (user=seanjc job=sendgmr) by 2002:a25:5f46:: with SMTP id h6mr16551423ybm.255.1616725245154; Thu, 25 Mar 2021 19:20:45 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 25 Mar 2021 19:19:54 -0700 In-Reply-To: <20210326021957.1424875-1-seanjc@google.com> Message-Id: <20210326021957.1424875-16-seanjc@google.com> Mime-Version: 1.0 References: <20210326021957.1424875-1-seanjc@google.com> X-Mailer: git-send-email 2.31.0.291.g576ba9dcdaf-goog Subject: [PATCH 15/18] KVM: Take mmu_lock when handling MMU notifier iff the hva hits a memslot From: Sean Christopherson To: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Paolo Bonzini Cc: James Morse , Julien Thierry , Suzuki K Poulose , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Defer acquiring mmu_lock in the MMU notifier paths until a "hit" has been detected in the memslots, i.e. don't take the lock for notifications that don't affect the guest. For small VMs, spurious locking is a minor annoyance. And for "volatile" setups where the majority of notifications _are_ relevant, this barely qualifies as an optimization. But, for large VMs (hundreds of threads) with static setups, e.g. no page migration, no swapping, etc..., the vast majority of MMU notifier callbacks will be unrelated to the guest, e.g. will often be in response to the userspace VMM adjusting its own virtual address space. In such large VMs, acquiring mmu_lock can be painful as it blocks vCPUs from handling page faults. In some scenarios it can even be "fatal" in the sense that it causes unacceptable brownouts, e.g. when rebuilding huge pages after live migration, a significant percentage of vCPUs will be attempting to handle page faults. x86's TDP MMU implementation is especially susceptible to spurious locking due it taking mmu_lock for read when handling page faults. Because rwlock is fair, a single writer will stall future readers, while the writer is itself stalled waiting for in-progress readers to complete. This is exacerbated by the MMU notifiers often firing multiple times in quick succession, e.g. moving a page will (always?) invoke three separate notifiers: .invalidate_range_start(), invalidate_range_end(), and .change_pte(). Unnecessarily taking mmu_lock each time means even a single spurious sequence can be problematic. Note, this optimizes only the unpaired callbacks. Optimizing the .invalidate_range_{start,end}() pairs is more complex and will be done in a future patch. Suggested-by: Ben Gardon Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 34 ++++++++++++++++------------------ 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index bfa43eea891a..0c2aff8a4aa1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -458,6 +458,7 @@ struct kvm_hva_range { unsigned long end; pte_t pte; hva_handler_t handler; + bool caller_locked; bool flush_on_ret; bool may_block; }; @@ -465,14 +466,12 @@ struct kvm_hva_range { static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, const struct kvm_hva_range *range) { - struct kvm_memory_slot *slot; - struct kvm_memslots *slots; + bool ret = false, locked = range->caller_locked; struct kvm_gfn_range gfn_range; - bool ret = false; + struct kvm_memory_slot *slot; + struct kvm_memslots *slots; int i, idx; - lockdep_assert_held_write(&kvm->mmu_lock); - idx = srcu_read_lock(&kvm->srcu); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { @@ -503,6 +502,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot); gfn_range.slot = slot; + if (!locked) { + locked = true; + KVM_MMU_LOCK(kvm); + } ret |= range->handler(kvm, &gfn_range); } } @@ -510,6 +513,9 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, if (range->flush_on_ret && (ret || kvm->tlbs_dirty)) kvm_flush_remote_tlbs(kvm); + if (locked && !range->caller_locked) + KVM_MMU_UNLOCK(kvm); + srcu_read_unlock(&kvm->srcu, idx); /* The notifiers are averse to booleans. :-( */ @@ -528,16 +534,11 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .end = end, .pte = pte, .handler = handler, + .caller_locked = false, .flush_on_ret = true, .may_block = false, }; - int ret; - - KVM_MMU_LOCK(kvm); - ret = __kvm_handle_hva_range(kvm, &range); - KVM_MMU_UNLOCK(kvm); - - return ret; + return __kvm_handle_hva_range(kvm, &range); } static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn, @@ -551,16 +552,12 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .end = end, .pte = __pte(0), .handler = handler, + .caller_locked = false, .flush_on_ret = false, .may_block = false, }; - int ret; - KVM_MMU_LOCK(kvm); - ret = __kvm_handle_hva_range(kvm, &range); - KVM_MMU_UNLOCK(kvm); - - return ret; + return __kvm_handle_hva_range(kvm, &range); } static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, struct mm_struct *mm, @@ -581,6 +578,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, .end = range->end, .pte = __pte(0), .handler = kvm_unmap_gfn_range, + .caller_locked = true, .flush_on_ret = true, .may_block = mmu_notifier_range_blockable(range), }; -- 2.31.0.291.g576ba9dcdaf-goog