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 A3D67C433E6 for ; Fri, 26 Mar 2021 02:21:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8548061A44 for ; Fri, 26 Mar 2021 02:21:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231239AbhCZCVZ (ORCPT ); Thu, 25 Mar 2021 22:21:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35460 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231362AbhCZCUs (ORCPT ); Thu, 25 Mar 2021 22:20:48 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B965C061763 for ; Thu, 25 Mar 2021 19:20:48 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id w7so6424771ybq.4 for ; Thu, 25 Mar 2021 19:20:48 -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=MPc01z273sWoKotX8Qo0ceeU7wfqOn4djZ7tWO1HqQw=; b=oRZN7Er/jTO0JwT0oKSSka1YhWa2PlQIYMpGu92ncg6e1E3YFeTMq/MUwiylTuzqmy 6szo2kBiPHr7OyPl8HPKwOAgMxv+2EZBT+gM6NfZHo/Y4LQ4pzeXgDuVA6YL7y3+ruFQ Pjt5BRi9G0XgHWVYPdHTwgWnr01QQmXF6ndEMk11Jk2C+v5gtkez0qZlxxOpQOTG2am7 vnXE1P7+7NflNJgvaK22y+ku115V63osmcvdIM8lBUsuZFn7fLFk1uFd5BK+s71loL/L y9JtTgFUPEdDwTzXfFq+DRjsA9VSfj7kFsh6laahlqZQf/wdRe2ZRt/5P5n4sxt74mZT 9CAA== 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=MPc01z273sWoKotX8Qo0ceeU7wfqOn4djZ7tWO1HqQw=; b=nm33wuWGJfCiDVYdIR5y6akJedJFQE452qHJYoDMtn+hYC/wMM0AHRaM8KTjwO0d60 PVdF+iJSwSWA4lRFyIgBEibppNCmx3hs57zbXKXm9OgJKRmYEWfwBP+DOVTE8x88HKQN KmSfQKW71Bz6fOWO11DP/LCvwEnQrHRHgqpNF6qWsEjO0Ykj1QzW5ciTB9wg5P88zBmo +lHbIVium1OMWDgBqQQS3sQYrpbU8+fs0GvptTTtNNsJnlZT3TXRJ8IDJFGetLSrJowB ZKRj1qXnMpl0xTRyQIVmTV61MC8f8dGqY3t3knHzwSm73tgmLYVYtNzCJ8O9hSnwpn6i CxPg== X-Gm-Message-State: AOAM530hOsDqs/R8OpnzXkOa9MCYGEWJ97uiQ0egUTltRNFKmCHPdSR/ Cg9yOg5dm4c27OyyrSoMwAhJWAVg5KQ= X-Google-Smtp-Source: ABdhPJxX4MIsUEfB0Uh5/Djl4Kfv52yIB+lxKn2YepBTM+7LrWOGL64erI1hTb+J5ndxOUOKW1qXZZpbd+A= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:f:10:b1bb:fab2:7ef5:fc7d]) (user=seanjc job=sendgmr) by 2002:a05:6902:4e9:: with SMTP id w9mr16839298ybs.409.1616725247572; Thu, 25 Mar 2021 19:20:47 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 25 Mar 2021 19:19:55 -0700 In-Reply-To: <20210326021957.1424875-1-seanjc@google.com> Message-Id: <20210326021957.1424875-17-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 16/18] KVM: Don't take mmu_lock for range invalidation unless necessary 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-kernel@vger.kernel.org Avoid taking mmu_lock for unrelated .invalidate_range_{start,end}() notifications. Because mmu_notifier_count must be modified while holding mmu_lock for write, and must always be paired across start->end to stay balanced, lock elision must happen in both or none. To meet that requirement, add a rwsem to prevent memslot updates across range_start() and range_end(). For notifiers that disallow blocking, e.g. OOM reaping, simply go down the slow path of unconditionally acquiring mmu_lock. The sane alternative would be to try to acquire the lock and force the notifier to retry on failure. But since OOM is currently the _only_ scenario where blocking is disallowed attempting to optimize a guest that has been marked for death is pointless. Note, technically flag-only memslot updates could be allowed in parallel, but stalling a memslot update for a relatively short amount of time is not a scalability issue, and this is all more than complex enough. Based heavily on code from Ben Gardon. Suggested-by: Ben Gardon Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 8 +- virt/kvm/kvm_main.c | 174 ++++++++++++++++++++++++++++++--------- 2 files changed, 142 insertions(+), 40 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 40ac2d40bb5a..2cc0f87d936e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -523,6 +523,7 @@ struct kvm { long mmu_notifier_count; unsigned long mmu_notifier_range_start; unsigned long mmu_notifier_range_end; + struct rw_semaphore mmu_notifier_slots_lock; #endif long tlbs_dirty; struct list_head devices; @@ -660,8 +661,11 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { as_id = array_index_nospec(as_id, KVM_ADDRESS_SPACE_NUM); return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock) || - !refcount_read(&kvm->users_count)); + lockdep_is_held(&kvm->slots_lock) || +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + lockdep_is_held(&kvm->mmu_notifier_slots_lock) || +#endif + !refcount_read(&kvm->users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0c2aff8a4aa1..9ebc6d3e4a21 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -453,20 +453,56 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn, typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range); +typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start, + unsigned long end); + struct kvm_hva_range { unsigned long start; unsigned long end; pte_t pte; hva_handler_t handler; - bool caller_locked; + on_lock_fn_t on_lock; + bool must_lock; bool flush_on_ret; bool may_block; }; +/* + * Use a dedicated stub instead of NULL to indicate that there is no callback + * function/handler. The compiler technically can't guarantee that a real + * function will have a non-zero address, and so it will generate code to + * check for !NULL, whereas comparing against a stub will be elided at compile + * time (unless the compiler is getting long in the tooth, e.g. gcc 4.9). + */ +static void kvm_null_fn(void) +{ + +} +#define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn) + + +/* Acquire mmu_lock if necessary. Returns %true if @handler is "null" */ +static __always_inline bool kvm_mmu_lock_and_check_handler(struct kvm *kvm, + const struct kvm_hva_range *range, + bool *locked) +{ + if (*locked) + return false; + + *locked = true; + + KVM_MMU_LOCK(kvm); + + if (!IS_KVM_NULL_FN(range->on_lock)) + range->on_lock(kvm, range->start, range->end); + + return IS_KVM_NULL_FN(range->handler); +} + static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, const struct kvm_hva_range *range) { - bool ret = false, locked = range->caller_locked; + bool ret = false, locked = false; struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; @@ -474,6 +510,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, idx = srcu_read_lock(&kvm->srcu); + if (range->must_lock && + kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { slots = __kvm_memslots(kvm, i); kvm_for_each_memslot(slot, slots) { @@ -502,10 +542,9 @@ 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); - } + if (kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + ret |= range->handler(kvm, &gfn_range); } } @@ -513,7 +552,8 @@ 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) +out_unlock: + if (locked) KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); @@ -534,10 +574,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .end = end, .pte = pte, .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = true, .may_block = false, }; + return __kvm_handle_hva_range(kvm, &range); } @@ -552,7 +594,8 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .end = end, .pte = __pte(0), .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = false, .may_block = false, }; @@ -569,23 +612,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); } -static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, - const struct mmu_notifier_range *range) +static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) { - struct kvm *kvm = mmu_notifier_to_kvm(mn); - const struct kvm_hva_range hva_range = { - .start = range->start, - .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), - }; - - trace_kvm_unmap_hva_range(range->start, range->end); - - KVM_MMU_LOCK(kvm); /* * The count increase must become visible at unlock time as no * spte can be established without taking the mmu_lock and @@ -593,8 +622,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, */ kvm->mmu_notifier_count++; if (likely(kvm->mmu_notifier_count == 1)) { - kvm->mmu_notifier_range_start = range->start; - kvm->mmu_notifier_range_end = range->end; + kvm->mmu_notifier_range_start = start; + kvm->mmu_notifier_range_end = end; } else { /* * Fully tracking multiple concurrent ranges has dimishing @@ -606,24 +635,54 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, * complete. */ kvm->mmu_notifier_range_start = - min(kvm->mmu_notifier_range_start, range->start); + min(kvm->mmu_notifier_range_start, start); kvm->mmu_notifier_range_end = - max(kvm->mmu_notifier_range_end, range->end); + max(kvm->mmu_notifier_range_end, end); } - - __kvm_handle_hva_range(kvm, &hva_range); - - KVM_MMU_UNLOCK(kvm); - - return 0; } -static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, +static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, const struct mmu_notifier_range *range) { + bool blockable = mmu_notifier_range_blockable(range); struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = kvm_unmap_gfn_range, + .on_lock = kvm_inc_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; - KVM_MMU_LOCK(kvm); + trace_kvm_unmap_hva_range(range->start, range->end); + + /* + * Prevent memslot modification between range_start() and range_end() + * so that conditionally locking provides the same result in both + * functions. Without that guarantee, the mmu_notifier_count + * adjustments will be imbalanced. + * + * Skip the memslot-lookup lock elision (set @must_lock above) to avoid + * having to take the semaphore on non-blockable calls, e.g. OOM kill. + * The complexity required to handle conditional locking for this case + * is not worth the marginal benefits, the VM is likely doomed anyways. + * + * Pairs with the unlock in range_end(). + */ + if (blockable) + down_read(&kvm->mmu_notifier_slots_lock); + + __kvm_handle_hva_range(kvm, &hva_range); + + return 0; +} + +static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) +{ /* * This sequence increase will notify the kvm page fault that * the page that is going to be mapped in the spte could have @@ -637,7 +696,29 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, * in conjunction with the smp_rmb in mmu_notifier_retry(). */ kvm->mmu_notifier_count--; - KVM_MMU_UNLOCK(kvm); +} + +static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, + const struct mmu_notifier_range *range) +{ + bool blockable = mmu_notifier_range_blockable(range); + struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = (void *)kvm_null_fn, + .on_lock = kvm_dec_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; + + __kvm_handle_hva_range(kvm, &hva_range); + + /* Pairs with the lock in range_start(). */ + if (blockable) + up_read(&kvm->mmu_notifier_slots_lock); BUG_ON(kvm->mmu_notifier_count < 0); } @@ -709,6 +790,8 @@ static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { static int kvm_init_mmu_notifier(struct kvm *kvm) { + init_rwsem(&kvm->mmu_notifier_slots_lock); + kvm->mmu_notifier.ops = &kvm_mmu_notifier_ops; return mmu_notifier_register(&kvm->mmu_notifier, current->mm); } @@ -971,6 +1054,15 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_coalesced_mmio_free(kvm); #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm); + /* + * Reset the lock used to prevent memslot updates between MMU notifier + * range_start and range_end. At this point no more MMU notifiers will + * run, but the lock could still be held if KVM's notifier was removed + * between range_start and range_end. No threads can be waiting on the + * lock as the last reference on KVM has been dropped. If the lock is + * still held, freeing memslots will deadlock. + */ + init_rwsem(&kvm->mmu_notifier_slots_lock); #else kvm_arch_flush_shadow_all(kvm); #endif @@ -1222,7 +1314,13 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS); slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS; +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + down_write(&kvm->mmu_notifier_slots_lock); +#endif rcu_assign_pointer(kvm->memslots[as_id], slots); +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + up_write(&kvm->mmu_notifier_slots_lock); +#endif synchronize_srcu_expedited(&kvm->srcu); /* -- 2.31.0.291.g576ba9dcdaf-goog 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=-16.5 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 D388CC433DB for ; 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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=MPc01z273sWoKotX8Qo0ceeU7wfqOn4djZ7tWO1HqQw=; b=OmoBu2ggA7ubaYMfGAkqX7tTd9ruRK9jfMG0XTdO5jB39i69v2IwrHI8UX0x96n3+P zMw7WPWdG20k05U4N+i3Y8lm+HpZmraPuw3puXc1OOdYjlttr7GXzyzEjTWcffARSC+U eQuebM+02bSMvaUv3fWKeBHbtJmSCAkTjIl40STjH7KFb0m/IzMAOk0NyQyZh9hgz0m8 6bZRkLjXR4gnfP+BqvcqY1de3rCPcjEzeb0HZo4QKY+GKsvX8YU1Swmma446Y1sf40L8 Res3j0QBeUPZ33gvf0+SOfEDyU/7wmO23NnQmqPHgdvitKgceB9Qr+4Lv4aAI4NYisbo shsA== X-Gm-Message-State: AOAM530CCzWJ8eIcGWiAeHqYs6Difrtr5Ac0yEjXJy0n+1Ny13S0qJ7z BssJqc30glS5xFP16K5U3yd+vh/M1ns= X-Google-Smtp-Source: ABdhPJxX4MIsUEfB0Uh5/Djl4Kfv52yIB+lxKn2YepBTM+7LrWOGL64erI1hTb+J5ndxOUOKW1qXZZpbd+A= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:f:10:b1bb:fab2:7ef5:fc7d]) (user=seanjc job=sendgmr) by 2002:a05:6902:4e9:: with SMTP id w9mr16839298ybs.409.1616725247572; Thu, 25 Mar 2021 19:20:47 -0700 (PDT) Date: Thu, 25 Mar 2021 19:19:55 -0700 In-Reply-To: <20210326021957.1424875-1-seanjc@google.com> Message-Id: <20210326021957.1424875-17-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 16/18] KVM: Don't take mmu_lock for range invalidation unless necessary From: Sean Christopherson To: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Paolo Bonzini X-Mailman-Approved-At: Fri, 26 Mar 2021 09:54:23 -0400 Cc: Wanpeng Li , kvm@vger.kernel.org, Sean Christopherson , Joerg Roedel , linux-mips@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Ben Gardon , Vitaly Kuznetsov , kvmarm@lists.cs.columbia.edu, Jim Mattson X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list Reply-To: Sean Christopherson List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Avoid taking mmu_lock for unrelated .invalidate_range_{start,end}() notifications. Because mmu_notifier_count must be modified while holding mmu_lock for write, and must always be paired across start->end to stay balanced, lock elision must happen in both or none. To meet that requirement, add a rwsem to prevent memslot updates across range_start() and range_end(). For notifiers that disallow blocking, e.g. OOM reaping, simply go down the slow path of unconditionally acquiring mmu_lock. The sane alternative would be to try to acquire the lock and force the notifier to retry on failure. But since OOM is currently the _only_ scenario where blocking is disallowed attempting to optimize a guest that has been marked for death is pointless. Note, technically flag-only memslot updates could be allowed in parallel, but stalling a memslot update for a relatively short amount of time is not a scalability issue, and this is all more than complex enough. Based heavily on code from Ben Gardon. Suggested-by: Ben Gardon Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 8 +- virt/kvm/kvm_main.c | 174 ++++++++++++++++++++++++++++++--------- 2 files changed, 142 insertions(+), 40 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 40ac2d40bb5a..2cc0f87d936e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -523,6 +523,7 @@ struct kvm { long mmu_notifier_count; unsigned long mmu_notifier_range_start; unsigned long mmu_notifier_range_end; + struct rw_semaphore mmu_notifier_slots_lock; #endif long tlbs_dirty; struct list_head devices; @@ -660,8 +661,11 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { as_id = array_index_nospec(as_id, KVM_ADDRESS_SPACE_NUM); return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock) || - !refcount_read(&kvm->users_count)); + lockdep_is_held(&kvm->slots_lock) || +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + lockdep_is_held(&kvm->mmu_notifier_slots_lock) || +#endif + !refcount_read(&kvm->users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0c2aff8a4aa1..9ebc6d3e4a21 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -453,20 +453,56 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn, typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range); +typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start, + unsigned long end); + struct kvm_hva_range { unsigned long start; unsigned long end; pte_t pte; hva_handler_t handler; - bool caller_locked; + on_lock_fn_t on_lock; + bool must_lock; bool flush_on_ret; bool may_block; }; +/* + * Use a dedicated stub instead of NULL to indicate that there is no callback + * function/handler. The compiler technically can't guarantee that a real + * function will have a non-zero address, and so it will generate code to + * check for !NULL, whereas comparing against a stub will be elided at compile + * time (unless the compiler is getting long in the tooth, e.g. gcc 4.9). + */ +static void kvm_null_fn(void) +{ + +} +#define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn) + + +/* Acquire mmu_lock if necessary. Returns %true if @handler is "null" */ +static __always_inline bool kvm_mmu_lock_and_check_handler(struct kvm *kvm, + const struct kvm_hva_range *range, + bool *locked) +{ + if (*locked) + return false; + + *locked = true; + + KVM_MMU_LOCK(kvm); + + if (!IS_KVM_NULL_FN(range->on_lock)) + range->on_lock(kvm, range->start, range->end); + + return IS_KVM_NULL_FN(range->handler); +} + static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, const struct kvm_hva_range *range) { - bool ret = false, locked = range->caller_locked; + bool ret = false, locked = false; struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; @@ -474,6 +510,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, idx = srcu_read_lock(&kvm->srcu); + if (range->must_lock && + kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { slots = __kvm_memslots(kvm, i); kvm_for_each_memslot(slot, slots) { @@ -502,10 +542,9 @@ 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); - } + if (kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + ret |= range->handler(kvm, &gfn_range); } } @@ -513,7 +552,8 @@ 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) +out_unlock: + if (locked) KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); @@ -534,10 +574,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .end = end, .pte = pte, .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = true, .may_block = false, }; + return __kvm_handle_hva_range(kvm, &range); } @@ -552,7 +594,8 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .end = end, .pte = __pte(0), .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = false, .may_block = false, }; @@ -569,23 +612,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); } -static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, - const struct mmu_notifier_range *range) +static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) { - struct kvm *kvm = mmu_notifier_to_kvm(mn); - const struct kvm_hva_range hva_range = { - .start = range->start, - .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), - }; - - trace_kvm_unmap_hva_range(range->start, range->end); - - KVM_MMU_LOCK(kvm); /* * The count increase must become visible at unlock time as no * spte can be established without taking the mmu_lock and @@ -593,8 +622,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, */ kvm->mmu_notifier_count++; if (likely(kvm->mmu_notifier_count == 1)) { - kvm->mmu_notifier_range_start = range->start; - kvm->mmu_notifier_range_end = range->end; + kvm->mmu_notifier_range_start = start; + kvm->mmu_notifier_range_end = end; } else { /* * Fully tracking multiple concurrent ranges has dimishing @@ -606,24 +635,54 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, * complete. */ kvm->mmu_notifier_range_start = - min(kvm->mmu_notifier_range_start, range->start); + min(kvm->mmu_notifier_range_start, start); kvm->mmu_notifier_range_end = - max(kvm->mmu_notifier_range_end, range->end); + max(kvm->mmu_notifier_range_end, end); } - - __kvm_handle_hva_range(kvm, &hva_range); - - KVM_MMU_UNLOCK(kvm); - - return 0; } -static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, +static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, const struct mmu_notifier_range *range) { + bool blockable = mmu_notifier_range_blockable(range); struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = kvm_unmap_gfn_range, + .on_lock = kvm_inc_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; - KVM_MMU_LOCK(kvm); + trace_kvm_unmap_hva_range(range->start, range->end); + + /* + * Prevent memslot modification between range_start() and range_end() + * so that conditionally locking provides the same result in both + * functions. Without that guarantee, the mmu_notifier_count + * adjustments will be imbalanced. + * + * Skip the memslot-lookup lock elision (set @must_lock above) to avoid + * having to take the semaphore on non-blockable calls, e.g. OOM kill. + * The complexity required to handle conditional locking for this case + * is not worth the marginal benefits, the VM is likely doomed anyways. + * + * Pairs with the unlock in range_end(). + */ + if (blockable) + down_read(&kvm->mmu_notifier_slots_lock); + + __kvm_handle_hva_range(kvm, &hva_range); + + return 0; +} + +static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) +{ /* * This sequence increase will notify the kvm page fault that * the page that is going to be mapped in the spte could have @@ -637,7 +696,29 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, * in conjunction with the smp_rmb in mmu_notifier_retry(). */ kvm->mmu_notifier_count--; - KVM_MMU_UNLOCK(kvm); +} + +static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, + const struct mmu_notifier_range *range) +{ + bool blockable = mmu_notifier_range_blockable(range); + struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = (void *)kvm_null_fn, + .on_lock = kvm_dec_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; + + __kvm_handle_hva_range(kvm, &hva_range); + + /* Pairs with the lock in range_start(). */ + if (blockable) + up_read(&kvm->mmu_notifier_slots_lock); BUG_ON(kvm->mmu_notifier_count < 0); } @@ -709,6 +790,8 @@ static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { static int kvm_init_mmu_notifier(struct kvm *kvm) { + init_rwsem(&kvm->mmu_notifier_slots_lock); + kvm->mmu_notifier.ops = &kvm_mmu_notifier_ops; return mmu_notifier_register(&kvm->mmu_notifier, current->mm); } @@ -971,6 +1054,15 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_coalesced_mmio_free(kvm); #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm); + /* + * Reset the lock used to prevent memslot updates between MMU notifier + * range_start and range_end. At this point no more MMU notifiers will + * run, but the lock could still be held if KVM's notifier was removed + * between range_start and range_end. No threads can be waiting on the + * lock as the last reference on KVM has been dropped. If the lock is + * still held, freeing memslots will deadlock. + */ + init_rwsem(&kvm->mmu_notifier_slots_lock); #else kvm_arch_flush_shadow_all(kvm); #endif @@ -1222,7 +1314,13 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS); slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS; +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + down_write(&kvm->mmu_notifier_slots_lock); +#endif rcu_assign_pointer(kvm->memslots[as_id], slots); +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + up_write(&kvm->mmu_notifier_slots_lock); +#endif synchronize_srcu_expedited(&kvm->srcu); /* -- 2.31.0.291.g576ba9dcdaf-goog _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-17.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 F127BC433C1 for ; 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Thu, 25 Mar 2021 19:20:47 -0700 (PDT) Date: Thu, 25 Mar 2021 19:19:55 -0700 In-Reply-To: <20210326021957.1424875-1-seanjc@google.com> Message-Id: <20210326021957.1424875-17-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 16/18] KVM: Don't take mmu_lock for range invalidation unless necessary 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210326_022050_723599_FB27E37A X-CRM114-Status: GOOD ( 29.48 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Avoid taking mmu_lock for unrelated .invalidate_range_{start,end}() notifications. Because mmu_notifier_count must be modified while holding mmu_lock for write, and must always be paired across start->end to stay balanced, lock elision must happen in both or none. To meet that requirement, add a rwsem to prevent memslot updates across range_start() and range_end(). For notifiers that disallow blocking, e.g. OOM reaping, simply go down the slow path of unconditionally acquiring mmu_lock. The sane alternative would be to try to acquire the lock and force the notifier to retry on failure. But since OOM is currently the _only_ scenario where blocking is disallowed attempting to optimize a guest that has been marked for death is pointless. Note, technically flag-only memslot updates could be allowed in parallel, but stalling a memslot update for a relatively short amount of time is not a scalability issue, and this is all more than complex enough. Based heavily on code from Ben Gardon. Suggested-by: Ben Gardon Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 8 +- virt/kvm/kvm_main.c | 174 ++++++++++++++++++++++++++++++--------- 2 files changed, 142 insertions(+), 40 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 40ac2d40bb5a..2cc0f87d936e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -523,6 +523,7 @@ struct kvm { long mmu_notifier_count; unsigned long mmu_notifier_range_start; unsigned long mmu_notifier_range_end; + struct rw_semaphore mmu_notifier_slots_lock; #endif long tlbs_dirty; struct list_head devices; @@ -660,8 +661,11 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { as_id = array_index_nospec(as_id, KVM_ADDRESS_SPACE_NUM); return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock) || - !refcount_read(&kvm->users_count)); + lockdep_is_held(&kvm->slots_lock) || +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + lockdep_is_held(&kvm->mmu_notifier_slots_lock) || +#endif + !refcount_read(&kvm->users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0c2aff8a4aa1..9ebc6d3e4a21 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -453,20 +453,56 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn, typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range); +typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start, + unsigned long end); + struct kvm_hva_range { unsigned long start; unsigned long end; pte_t pte; hva_handler_t handler; - bool caller_locked; + on_lock_fn_t on_lock; + bool must_lock; bool flush_on_ret; bool may_block; }; +/* + * Use a dedicated stub instead of NULL to indicate that there is no callback + * function/handler. The compiler technically can't guarantee that a real + * function will have a non-zero address, and so it will generate code to + * check for !NULL, whereas comparing against a stub will be elided at compile + * time (unless the compiler is getting long in the tooth, e.g. gcc 4.9). + */ +static void kvm_null_fn(void) +{ + +} +#define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn) + + +/* Acquire mmu_lock if necessary. Returns %true if @handler is "null" */ +static __always_inline bool kvm_mmu_lock_and_check_handler(struct kvm *kvm, + const struct kvm_hva_range *range, + bool *locked) +{ + if (*locked) + return false; + + *locked = true; + + KVM_MMU_LOCK(kvm); + + if (!IS_KVM_NULL_FN(range->on_lock)) + range->on_lock(kvm, range->start, range->end); + + return IS_KVM_NULL_FN(range->handler); +} + static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, const struct kvm_hva_range *range) { - bool ret = false, locked = range->caller_locked; + bool ret = false, locked = false; struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; @@ -474,6 +510,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, idx = srcu_read_lock(&kvm->srcu); + if (range->must_lock && + kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { slots = __kvm_memslots(kvm, i); kvm_for_each_memslot(slot, slots) { @@ -502,10 +542,9 @@ 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); - } + if (kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + ret |= range->handler(kvm, &gfn_range); } } @@ -513,7 +552,8 @@ 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) +out_unlock: + if (locked) KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); @@ -534,10 +574,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .end = end, .pte = pte, .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = true, .may_block = false, }; + return __kvm_handle_hva_range(kvm, &range); } @@ -552,7 +594,8 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .end = end, .pte = __pte(0), .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = false, .may_block = false, }; @@ -569,23 +612,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); } -static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, - const struct mmu_notifier_range *range) +static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) { - struct kvm *kvm = mmu_notifier_to_kvm(mn); - const struct kvm_hva_range hva_range = { - .start = range->start, - .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), - }; - - trace_kvm_unmap_hva_range(range->start, range->end); - - KVM_MMU_LOCK(kvm); /* * The count increase must become visible at unlock time as no * spte can be established without taking the mmu_lock and @@ -593,8 +622,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, */ kvm->mmu_notifier_count++; if (likely(kvm->mmu_notifier_count == 1)) { - kvm->mmu_notifier_range_start = range->start; - kvm->mmu_notifier_range_end = range->end; + kvm->mmu_notifier_range_start = start; + kvm->mmu_notifier_range_end = end; } else { /* * Fully tracking multiple concurrent ranges has dimishing @@ -606,24 +635,54 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, * complete. */ kvm->mmu_notifier_range_start = - min(kvm->mmu_notifier_range_start, range->start); + min(kvm->mmu_notifier_range_start, start); kvm->mmu_notifier_range_end = - max(kvm->mmu_notifier_range_end, range->end); + max(kvm->mmu_notifier_range_end, end); } - - __kvm_handle_hva_range(kvm, &hva_range); - - KVM_MMU_UNLOCK(kvm); - - return 0; } -static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, +static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, const struct mmu_notifier_range *range) { + bool blockable = mmu_notifier_range_blockable(range); struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = kvm_unmap_gfn_range, + .on_lock = kvm_inc_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; - KVM_MMU_LOCK(kvm); + trace_kvm_unmap_hva_range(range->start, range->end); + + /* + * Prevent memslot modification between range_start() and range_end() + * so that conditionally locking provides the same result in both + * functions. Without that guarantee, the mmu_notifier_count + * adjustments will be imbalanced. + * + * Skip the memslot-lookup lock elision (set @must_lock above) to avoid + * having to take the semaphore on non-blockable calls, e.g. OOM kill. + * The complexity required to handle conditional locking for this case + * is not worth the marginal benefits, the VM is likely doomed anyways. + * + * Pairs with the unlock in range_end(). + */ + if (blockable) + down_read(&kvm->mmu_notifier_slots_lock); + + __kvm_handle_hva_range(kvm, &hva_range); + + return 0; +} + +static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) +{ /* * This sequence increase will notify the kvm page fault that * the page that is going to be mapped in the spte could have @@ -637,7 +696,29 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, * in conjunction with the smp_rmb in mmu_notifier_retry(). */ kvm->mmu_notifier_count--; - KVM_MMU_UNLOCK(kvm); +} + +static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, + const struct mmu_notifier_range *range) +{ + bool blockable = mmu_notifier_range_blockable(range); + struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = (void *)kvm_null_fn, + .on_lock = kvm_dec_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; + + __kvm_handle_hva_range(kvm, &hva_range); + + /* Pairs with the lock in range_start(). */ + if (blockable) + up_read(&kvm->mmu_notifier_slots_lock); BUG_ON(kvm->mmu_notifier_count < 0); } @@ -709,6 +790,8 @@ static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { static int kvm_init_mmu_notifier(struct kvm *kvm) { + init_rwsem(&kvm->mmu_notifier_slots_lock); + kvm->mmu_notifier.ops = &kvm_mmu_notifier_ops; return mmu_notifier_register(&kvm->mmu_notifier, current->mm); } @@ -971,6 +1054,15 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_coalesced_mmio_free(kvm); #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm); + /* + * Reset the lock used to prevent memslot updates between MMU notifier + * range_start and range_end. At this point no more MMU notifiers will + * run, but the lock could still be held if KVM's notifier was removed + * between range_start and range_end. No threads can be waiting on the + * lock as the last reference on KVM has been dropped. If the lock is + * still held, freeing memslots will deadlock. + */ + init_rwsem(&kvm->mmu_notifier_slots_lock); #else kvm_arch_flush_shadow_all(kvm); #endif @@ -1222,7 +1314,13 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS); slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS; +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + down_write(&kvm->mmu_notifier_slots_lock); +#endif rcu_assign_pointer(kvm->memslots[as_id], slots); +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + up_write(&kvm->mmu_notifier_slots_lock); +#endif synchronize_srcu_expedited(&kvm->srcu); /* -- 2.31.0.291.g576ba9dcdaf-goog _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Date: Fri, 26 Mar 2021 02:19:55 +0000 Subject: [PATCH 16/18] KVM: Don't take mmu_lock for range invalidation unless necessary Message-Id: <20210326021957.1424875-17-seanjc@google.com> List-Id: References: <20210326021957.1424875-1-seanjc@google.com> In-Reply-To: <20210326021957.1424875-1-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 Avoid taking mmu_lock for unrelated .invalidate_range_{start,end}() notifications. Because mmu_notifier_count must be modified while holding mmu_lock for write, and must always be paired across start->end to stay balanced, lock elision must happen in both or none. To meet that requirement, add a rwsem to prevent memslot updates across range_start() and range_end(). For notifiers that disallow blocking, e.g. OOM reaping, simply go down the slow path of unconditionally acquiring mmu_lock. The sane alternative would be to try to acquire the lock and force the notifier to retry on failure. But since OOM is currently the _only_ scenario where blocking is disallowed attempting to optimize a guest that has been marked for death is pointless. Note, technically flag-only memslot updates could be allowed in parallel, but stalling a memslot update for a relatively short amount of time is not a scalability issue, and this is all more than complex enough. Based heavily on code from Ben Gardon. Suggested-by: Ben Gardon Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 8 +- virt/kvm/kvm_main.c | 174 ++++++++++++++++++++++++++++++--------- 2 files changed, 142 insertions(+), 40 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 40ac2d40bb5a..2cc0f87d936e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -523,6 +523,7 @@ struct kvm { long mmu_notifier_count; unsigned long mmu_notifier_range_start; unsigned long mmu_notifier_range_end; + struct rw_semaphore mmu_notifier_slots_lock; #endif long tlbs_dirty; struct list_head devices; @@ -660,8 +661,11 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) { as_id = array_index_nospec(as_id, KVM_ADDRESS_SPACE_NUM); return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, - lockdep_is_held(&kvm->slots_lock) || - !refcount_read(&kvm->users_count)); + lockdep_is_held(&kvm->slots_lock) || +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + lockdep_is_held(&kvm->mmu_notifier_slots_lock) || +#endif + !refcount_read(&kvm->users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0c2aff8a4aa1..9ebc6d3e4a21 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -453,20 +453,56 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn, typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range); +typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start, + unsigned long end); + struct kvm_hva_range { unsigned long start; unsigned long end; pte_t pte; hva_handler_t handler; - bool caller_locked; + on_lock_fn_t on_lock; + bool must_lock; bool flush_on_ret; bool may_block; }; +/* + * Use a dedicated stub instead of NULL to indicate that there is no callback + * function/handler. The compiler technically can't guarantee that a real + * function will have a non-zero address, and so it will generate code to + * check for !NULL, whereas comparing against a stub will be elided at compile + * time (unless the compiler is getting long in the tooth, e.g. gcc 4.9). + */ +static void kvm_null_fn(void) +{ + +} +#define IS_KVM_NULL_FN(fn) ((fn) = (void *)kvm_null_fn) + + +/* Acquire mmu_lock if necessary. Returns %true if @handler is "null" */ +static __always_inline bool kvm_mmu_lock_and_check_handler(struct kvm *kvm, + const struct kvm_hva_range *range, + bool *locked) +{ + if (*locked) + return false; + + *locked = true; + + KVM_MMU_LOCK(kvm); + + if (!IS_KVM_NULL_FN(range->on_lock)) + range->on_lock(kvm, range->start, range->end); + + return IS_KVM_NULL_FN(range->handler); +} + static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, const struct kvm_hva_range *range) { - bool ret = false, locked = range->caller_locked; + bool ret = false, locked = false; struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; @@ -474,6 +510,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, idx = srcu_read_lock(&kvm->srcu); + if (range->must_lock && + kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { slots = __kvm_memslots(kvm, i); kvm_for_each_memslot(slot, slots) { @@ -502,10 +542,9 @@ 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); - } + if (kvm_mmu_lock_and_check_handler(kvm, range, &locked)) + goto out_unlock; + ret |= range->handler(kvm, &gfn_range); } } @@ -513,7 +552,8 @@ 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) +out_unlock: + if (locked) KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); @@ -534,10 +574,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .end = end, .pte = pte, .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = true, .may_block = false, }; + return __kvm_handle_hva_range(kvm, &range); } @@ -552,7 +594,8 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .end = end, .pte = __pte(0), .handler = handler, - .caller_locked = false, + .on_lock = (void *)kvm_null_fn, + .must_lock = false, .flush_on_ret = false, .may_block = false, }; @@ -569,23 +612,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); } -static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, - const struct mmu_notifier_range *range) +static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) { - struct kvm *kvm = mmu_notifier_to_kvm(mn); - const struct kvm_hva_range hva_range = { - .start = range->start, - .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), - }; - - trace_kvm_unmap_hva_range(range->start, range->end); - - KVM_MMU_LOCK(kvm); /* * The count increase must become visible at unlock time as no * spte can be established without taking the mmu_lock and @@ -593,8 +622,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, */ kvm->mmu_notifier_count++; if (likely(kvm->mmu_notifier_count = 1)) { - kvm->mmu_notifier_range_start = range->start; - kvm->mmu_notifier_range_end = range->end; + kvm->mmu_notifier_range_start = start; + kvm->mmu_notifier_range_end = end; } else { /* * Fully tracking multiple concurrent ranges has dimishing @@ -606,24 +635,54 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, * complete. */ kvm->mmu_notifier_range_start - min(kvm->mmu_notifier_range_start, range->start); + min(kvm->mmu_notifier_range_start, start); kvm->mmu_notifier_range_end - max(kvm->mmu_notifier_range_end, range->end); + max(kvm->mmu_notifier_range_end, end); } - - __kvm_handle_hva_range(kvm, &hva_range); - - KVM_MMU_UNLOCK(kvm); - - return 0; } -static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, +static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, const struct mmu_notifier_range *range) { + bool blockable = mmu_notifier_range_blockable(range); struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = kvm_unmap_gfn_range, + .on_lock = kvm_inc_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; - KVM_MMU_LOCK(kvm); + trace_kvm_unmap_hva_range(range->start, range->end); + + /* + * Prevent memslot modification between range_start() and range_end() + * so that conditionally locking provides the same result in both + * functions. Without that guarantee, the mmu_notifier_count + * adjustments will be imbalanced. + * + * Skip the memslot-lookup lock elision (set @must_lock above) to avoid + * having to take the semaphore on non-blockable calls, e.g. OOM kill. + * The complexity required to handle conditional locking for this case + * is not worth the marginal benefits, the VM is likely doomed anyways. + * + * Pairs with the unlock in range_end(). + */ + if (blockable) + down_read(&kvm->mmu_notifier_slots_lock); + + __kvm_handle_hva_range(kvm, &hva_range); + + return 0; +} + +static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start, + unsigned long end) +{ /* * This sequence increase will notify the kvm page fault that * the page that is going to be mapped in the spte could have @@ -637,7 +696,29 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, * in conjunction with the smp_rmb in mmu_notifier_retry(). */ kvm->mmu_notifier_count--; - KVM_MMU_UNLOCK(kvm); +} + +static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, + const struct mmu_notifier_range *range) +{ + bool blockable = mmu_notifier_range_blockable(range); + struct kvm *kvm = mmu_notifier_to_kvm(mn); + const struct kvm_hva_range hva_range = { + .start = range->start, + .end = range->end, + .pte = __pte(0), + .handler = (void *)kvm_null_fn, + .on_lock = kvm_dec_notifier_count, + .must_lock = !blockable, + .flush_on_ret = true, + .may_block = blockable, + }; + + __kvm_handle_hva_range(kvm, &hva_range); + + /* Pairs with the lock in range_start(). */ + if (blockable) + up_read(&kvm->mmu_notifier_slots_lock); BUG_ON(kvm->mmu_notifier_count < 0); } @@ -709,6 +790,8 @@ static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { static int kvm_init_mmu_notifier(struct kvm *kvm) { + init_rwsem(&kvm->mmu_notifier_slots_lock); + kvm->mmu_notifier.ops = &kvm_mmu_notifier_ops; return mmu_notifier_register(&kvm->mmu_notifier, current->mm); } @@ -971,6 +1054,15 @@ static void kvm_destroy_vm(struct kvm *kvm) kvm_coalesced_mmio_free(kvm); #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm); + /* + * Reset the lock used to prevent memslot updates between MMU notifier + * range_start and range_end. At this point no more MMU notifiers will + * run, but the lock could still be held if KVM's notifier was removed + * between range_start and range_end. No threads can be waiting on the + * lock as the last reference on KVM has been dropped. If the lock is + * still held, freeing memslots will deadlock. + */ + init_rwsem(&kvm->mmu_notifier_slots_lock); #else kvm_arch_flush_shadow_all(kvm); #endif @@ -1222,7 +1314,13 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS); slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS; +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + down_write(&kvm->mmu_notifier_slots_lock); +#endif rcu_assign_pointer(kvm->memslots[as_id], slots); +#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER) + up_write(&kvm->mmu_notifier_slots_lock); +#endif synchronize_srcu_expedited(&kvm->srcu); /* -- 2.31.0.291.g576ba9dcdaf-goog