From patchwork Fri Nov 4 15:14:54 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Emanuele Giuseppe Esposito X-Patchwork-Id: 13032165 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 906B3C433FE for ; Fri, 4 Nov 2022 15:16:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232467AbiKDPQI (ORCPT ); Fri, 4 Nov 2022 11:16:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232465AbiKDPP4 (ORCPT ); Fri, 4 Nov 2022 11:15:56 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 999BA5582 for ; Fri, 4 Nov 2022 08:15:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667574900; 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: in-reply-to:in-reply-to:references:references; bh=nMGhB+cIUztS62Zo93dN1SSLUlu0sn9Iy9UJXvUpLpc=; b=GesGpj2zUMszvu4tnIaCmIoCeJuu7NRGDUfRT5tfHZFchsRjnZL26osWv5Br6iO5tfKvrB z3YAObvFoq6F7u8USBlHucD52iHAZJ9sVaMzZsLRXhJ99LfnaHBzk/Ae3Tg9DaeBrHKGTO za+mty/zTaDhyLVOvpaj1T/tcuOmBco= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-158-swPDqkY4O0me1kburFFHTw-1; Fri, 04 Nov 2022 11:14:57 -0400 X-MC-Unique: swPDqkY4O0me1kburFFHTw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 362202999B2C; Fri, 4 Nov 2022 15:14:57 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id E7A92C2C8C5; Fri, 4 Nov 2022 15:14:56 +0000 (UTC) From: Emanuele Giuseppe Esposito To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Eduardo Habkost , Marcel Apfelbaum , =?utf-8?q?Philippe_Mathieu-D?= =?utf-8?q?aud=C3=A9?= , Yanan Wang , kvm@vger.kernel.org, David Hildenbrand , Emanuele Giuseppe Esposito Subject: [RFC PATCH 3/3] kvm: Atomic memslot updates Date: Fri, 4 Nov 2022 11:14:54 -0400 Message-Id: <20221104151454.136551-4-eesposit@redhat.com> In-Reply-To: <20221104151454.136551-1-eesposit@redhat.com> References: <20221104151454.136551-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: David Hildenbrand If we update an existing memslot (e.g., resize, split), we temporarily remove the memslot to re-add it immediately afterwards. These updates are not atomic, especially not for KVM VCPU threads, such that we can get spurious faults. Let's inhibit most KVM ioctls while performing relevant updates, such that we can perform the update just as if it would happen atomically without additional kernel support. We capture the add/del changes and apply them in the notifier commit stage instead. There, we can check for overlaps and perform the ioctl inhibiting only if really required (-> overlap). To keep things simple we don't perform additional checks that wouldn't actually result in an overlap -- such as !RAM memory regions in some cases (see kvm_set_phys_mem()). To minimize cache-line bouncing, use a separate indicator (in_ioctl_lock) per CPU. Also, make sure to hold the kvm_slots_lock while performing both actions (removing+re-adding). We have to wait until all IOCTLs were exited and block new ones from getting executed. Kick all CPUs, so they will exit the KVM_RUN ioctl. This approach cannot result in a deadlock as long as the inhibitor does not hold any locks that might hinder an IOCTL from getting finished and exited - something fairly unusual. The inhibitor will always hold the BQL. AFAIKs, one possible candidate would be userfaultfd. If a page cannot be placed (e.g., during postcopy), because we're waiting for a lock, or if the userfaultfd thread cannot process a fault, because it is waiting for a lock, there could be a deadlock. However, the BQL is not applicable here, because any other guest memory access while holding the BQL would already result in a deadlock. Nothing else in the kernel should block forever and wait for userspace intervention. Note: pause_all_vcpus()/resume_all_vcpus() or start_exclusive()/end_exclusive() cannot be used, as they either drop the BQL or require to be called without the BQL - something inhibitors cannot handle. We need a low-level locking mechanism that is deadlock-free even when not releasing the BQL. Signed-off-by: David Hildenbrand Signed-off-by: Emanuele Giuseppe Esposito Tested-by: Emanuele Giuseppe Esposito --- accel/kvm/kvm-all.c | 142 ++++++++++++++++++++++++++++++++++++--- include/sysemu/kvm_int.h | 8 +++ 2 files changed, 139 insertions(+), 11 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 48cdf1fecd..05b7aa5403 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -46,6 +46,7 @@ #include "sysemu/hw_accel.h" #include "kvm-cpus.h" #include "sysemu/dirtylimit.h" +#include "qemu/range.h" #include "hw/boards.h" #include "monitor/stats.h" @@ -1294,6 +1295,7 @@ void kvm_set_max_memslot_size(hwaddr max_slot_size) kvm_max_slot_size = max_slot_size; } +/* Called with KVMMemoryListener.slots_lock held */ static void kvm_set_phys_mem(KVMMemoryListener *kml, MemoryRegionSection *section, bool add) { @@ -1328,14 +1330,12 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml, ram = memory_region_get_ram_ptr(mr) + mr_offset; ram_start_offset = memory_region_get_ram_addr(mr) + mr_offset; - kvm_slots_lock(); - if (!add) { do { slot_size = MIN(kvm_max_slot_size, size); mem = kvm_lookup_matching_slot(kml, start_addr, slot_size); if (!mem) { - goto out; + return; } if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) { /* @@ -1373,7 +1373,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml, start_addr += slot_size; size -= slot_size; } while (size); - goto out; + return; } /* register the new slot */ @@ -1398,9 +1398,6 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml, ram += slot_size; size -= slot_size; } while (size); - -out: - kvm_slots_unlock(); } static void *kvm_dirty_ring_reaper_thread(void *data) @@ -1457,18 +1454,137 @@ static void kvm_region_add(MemoryListener *listener, MemoryRegionSection *section) { KVMMemoryListener *kml = container_of(listener, KVMMemoryListener, listener); + KVMMemoryUpdate *update; + + update = g_new0(KVMMemoryUpdate, 1); + update->section = memory_region_section_new_copy(section); - memory_region_ref(section->mr); - kvm_set_phys_mem(kml, section, true); + QSIMPLEQ_INSERT_TAIL(&kml->transaction_add, update, next); } static void kvm_region_del(MemoryListener *listener, MemoryRegionSection *section) { KVMMemoryListener *kml = container_of(listener, KVMMemoryListener, listener); + KVMMemoryUpdate *update; + + update = g_new0(KVMMemoryUpdate, 1); + update->section = memory_region_section_new_copy(section); + + QSIMPLEQ_INSERT_TAIL(&kml->transaction_del, update, next); +} + +static void kvm_ioctl_inhibit_begin(void) +{ + CPUState *cpu; + + /* + * We allow to inhibit only when holding the BQL, so we can identify + * when an inhibitor wants to issue an ioctl easily. + */ + g_assert(qemu_mutex_iothread_locked()); + + CPU_FOREACH(cpu) { + qemu_lockcnt_lock(&cpu->in_ioctl_lock); + } + qemu_lockcnt_lock(&kvm_in_ioctl_lock); - kvm_set_phys_mem(kml, section, false); - memory_region_unref(section->mr); + /* Inhibiting happens rarely, we can keep things simple and spin here. */ + while (true) { + bool any_cpu_in_ioctl = false; + + CPU_FOREACH(cpu) { + if (qemu_lockcnt_count(&cpu->in_ioctl_lock)) { + any_cpu_in_ioctl = true; + qemu_cpu_kick(cpu); + } + } + if (!any_cpu_in_ioctl && + !qemu_lockcnt_count(&kvm_in_ioctl_lock)) { + break; + } + g_usleep(100); + } +} + +static void kvm_ioctl_inhibit_end(void) +{ + CPUState *cpu; + + qemu_lockcnt_unlock(&kvm_in_ioctl_lock); + CPU_FOREACH(cpu) { + qemu_lockcnt_unlock(&cpu->in_ioctl_lock); + } +} + +static void kvm_region_commit(MemoryListener *listener) +{ + KVMMemoryListener *kml = container_of(listener, KVMMemoryListener, + listener); + KVMMemoryUpdate *u1, *u2; + bool need_inhibit = false; + + if (QSIMPLEQ_EMPTY(&kml->transaction_add) && + QSIMPLEQ_EMPTY(&kml->transaction_del)) { + return; + } + + /* + * We have to be careful when regions to add overlap with ranges to remove. + * We have to simulate atomic KVM memslot updates by making sure no ioctl() + * is currently active. + * + * The lists are order by addresses, so it's easy to find overlaps. + */ + u1 = QSIMPLEQ_FIRST(&kml->transaction_del); + u2 = QSIMPLEQ_FIRST(&kml->transaction_add); + while (u1 && u2) { + Range r1, r2; + + range_init_nofail(&r1, u1->section->offset_within_address_space, + int128_get64(u1->section->size)); + range_init_nofail(&r2, u2->section->offset_within_address_space, + int128_get64(u2->section->size)); + + if (range_overlaps_range(&r1, &r2)) { + need_inhibit = true; + break; + } + if (range_lob(&r1) < range_lob(&r2)) { + u1 = QSIMPLEQ_NEXT(u1, next); + } else { + u2 = QSIMPLEQ_NEXT(u2, next); + } + } + + + kvm_slots_lock(); + if (need_inhibit) { + kvm_ioctl_inhibit_begin(); + } + + /* Remove all memslots before adding the new ones. */ + QSIMPLEQ_FOREACH_SAFE(u1, &kml->transaction_del, next, u2) { + kvm_set_phys_mem(kml, u1->section, false); + memory_region_unref(u1->section->mr); + + QSIMPLEQ_REMOVE(&kml->transaction_del, u1, KVMMemoryUpdate, next); + memory_region_section_free_copy(u1->section); + g_free(u1); + } + QSIMPLEQ_FOREACH_SAFE(u1, &kml->transaction_add, next, u2) { + memory_region_ref(u1->section->mr); + kvm_set_phys_mem(kml, u1->section, true); + + QSIMPLEQ_REMOVE(&kml->transaction_add, u1, KVMMemoryUpdate, next); + memory_region_section_free_copy(u1->section); + g_free(u1); + } + + if (need_inhibit) { + kvm_ioctl_inhibit_end(); + } + kvm_slots_unlock(); } static void kvm_log_sync(MemoryListener *listener, @@ -1612,8 +1728,12 @@ void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml, kml->slots[i].slot = i; } + QSIMPLEQ_INIT(&kml->transaction_add); + QSIMPLEQ_INIT(&kml->transaction_del); + kml->listener.region_add = kvm_region_add; kml->listener.region_del = kvm_region_del; + kml->listener.commit = kvm_region_commit; kml->listener.log_start = kvm_log_start; kml->listener.log_stop = kvm_log_stop; kml->listener.priority = 10; diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h index 3b4adcdc10..5ea2d7924b 100644 --- a/include/sysemu/kvm_int.h +++ b/include/sysemu/kvm_int.h @@ -12,6 +12,7 @@ #include "exec/memory.h" #include "qapi/qapi-types-common.h" #include "qemu/accel.h" +#include "qemu/queue.h" #include "sysemu/kvm.h" typedef struct KVMSlot @@ -31,10 +32,17 @@ typedef struct KVMSlot ram_addr_t ram_start_offset; } KVMSlot; +typedef struct KVMMemoryUpdate { + QSIMPLEQ_ENTRY(KVMMemoryUpdate) next; + MemoryRegionSection *section; +} KVMMemoryUpdate; + typedef struct KVMMemoryListener { MemoryListener listener; KVMSlot *slots; int as_id; + QSIMPLEQ_HEAD(, KVMMemoryUpdate) transaction_add; + QSIMPLEQ_HEAD(, KVMMemoryUpdate) transaction_del; } KVMMemoryListener; #define KVM_MSI_HASHTAB_SIZE 256