From patchwork Thu Jan 12 16:44:03 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13098445 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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 471B9C54EBD for ; Thu, 12 Jan 2023 16:47:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pG0gq-0004Pn-6S; Thu, 12 Jan 2023 11:44:32 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pG0gn-0004N4-8m for qemu-devel@nongnu.org; Thu, 12 Jan 2023 11:44:29 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pG0gl-0000ff-35 for qemu-devel@nongnu.org; Thu, 12 Jan 2023 11:44:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673541866; 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=ND5/3wzgiVdYN1GjhHLtNjDLDUgoR37f88YPkJxXf2c=; b=SQa2PIQTHSoMsHXwoM1EeAtyT0DrGlLR6DUFdav5aS2dSzFTljH+AdhDlerTJpRlxPCS71 63/TRRkgtbdfPt9xuKLF+zUbt4URa6YycLVYNySfYMWwYTlkOErNUxAR3It8fEUCos+rM9 ms7KcsRx4PVRH7Imny0Nx5GL02MQJJE= 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-176-lkVRfhLrPr6paFe3uF6D7A-1; Thu, 12 Jan 2023 11:44:25 -0500 X-MC-Unique: lkVRfhLrPr6paFe3uF6D7A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C2D081C0899C for ; Thu, 12 Jan 2023 16:44:24 +0000 (UTC) Received: from t480s.fritz.box (unknown [10.39.193.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id C70A74078903; Thu, 12 Jan 2023 16:44:22 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Cc: David Hildenbrand , "Dr . David Alan Gilbert" , Juan Quintela , Peter Xu , "Michael S . Tsirkin" , Michal Privoznik , Jing Qi Subject: [PATCH v3 8/8] virtio-mem: Proper support for preallocation with migration Date: Thu, 12 Jan 2023 17:44:03 +0100 Message-Id: <20230112164403.105085-9-david@redhat.com> In-Reply-To: <20230112164403.105085-1-david@redhat.com> References: <20230112164403.105085-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Ordinary memory preallocation runs when QEMU starts up and creates the memory backends, before processing the incoming migration stream. With virtio-mem, we don't know which memory blocks to preallocate before migration started. Now that we migrate the virtio-mem bitmap early, before migrating any RAM content, we can safely preallocate memory for all plugged memory blocks before migrating any RAM content. This is especially relevant for the following cases: (1) User errors With hugetlb/files, if we don't have sufficient backend memory available on the migration destination, we'll crash QEMU (SIGBUS) during RAM migration when running out of backend memory. Preallocating memory before actual RAM migration allows for failing gracefully and informing the user about the setup problem. (2) Excluded memory ranges during migration For example, virtio-balloon free page hinting will exclude some pages from getting migrated. In that case, we won't crash during RAM migration, but later, when running the VM on the destination, which is bad. To fix this for new QEMU machines that migrate the bitmap early, preallocate the memory early, before any RAM migration. Warn with old QEMU machines. Getting postcopy right is a bit tricky, but we essentially now implement the same (problematic) preallocation logic as ordinary preallocation: preallocate memory early and discard it again before precopy starts. During ordinary preallocation, discarding of RAM happens when postcopy is advised. As the state (bitmap) is loaded after postcopy was advised but before postcopy starts listening, we have to discard memory we preallocated immediately again ourselves. Note that nothing (not even hugetlb reservations) guarantees for postcopy that backend memory (especially, hugetlb pages) are still free after they were freed ones while discarding RAM. Still, allocating that memory at least once helps catching some basic setup problems. Before this change, trying to restore a VM when insufficient hugetlb pages are around results in the process crashing to to a "Bus error" (SIGBUS). With this change, QEMU fails gracefully: qemu-system-x86_64: qemu_prealloc_mem: preallocating memory failed: Bad address qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:03.0/virtio-mem-device-early' qemu-system-x86_64: load of migration failed: Cannot allocate memory And we can even introspect the early migration data, including the bitmap: $ ./scripts/analyze-migration.py -f STATEFILE { "ram (2)": { "section sizes": { "0000:00:03.0/mem0": "0x0000000780000000", "0000:00:04.0/mem1": "0x0000000780000000", "pc.ram": "0x0000000100000000", "/rom@etc/acpi/tables": "0x0000000000020000", "pc.bios": "0x0000000000040000", "0000:00:02.0/e1000.rom": "0x0000000000040000", "pc.rom": "0x0000000000020000", "/rom@etc/table-loader": "0x0000000000001000", "/rom@etc/acpi/rsdp": "0x0000000000001000" } }, "0000:00:03.0/virtio-mem-device-early (51)": { "tmp": "00 00 00 01 40 00 00 00 00 00 00 07 80 00 00 00 00 00 00 00 00 20 00 00 00 00 00 00", "size": "0x0000000040000000", "bitmap": "ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [...] }, "0000:00:04.0/virtio-mem-device-early (53)": { "tmp": "00 00 00 08 c0 00 00 00 00 00 00 07 80 00 00 00 00 00 00 00 00 20 00 00 00 00 00 00", "size": "0x00000001fa400000", "bitmap": "ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [...] }, [...] Reported-by: Jing Qi Signed-off-by: David Hildenbrand Reviewed-by: Dr. David Alan Gilbert --- hw/virtio/virtio-mem.c | 87 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c index 51666baa01..4c3720249c 100644 --- a/hw/virtio/virtio-mem.c +++ b/hw/virtio/virtio-mem.c @@ -204,6 +204,30 @@ static int virtio_mem_for_each_unplugged_range(const VirtIOMEM *vmem, void *arg, return ret; } +static int virtio_mem_for_each_plugged_range(const VirtIOMEM *vmem, void *arg, + virtio_mem_range_cb cb) +{ + unsigned long first_bit, last_bit; + uint64_t offset, size; + int ret = 0; + + first_bit = find_first_bit(vmem->bitmap, vmem->bitmap_size); + while (first_bit < vmem->bitmap_size) { + offset = first_bit * vmem->block_size; + last_bit = find_next_zero_bit(vmem->bitmap, vmem->bitmap_size, + first_bit + 1) - 1; + size = (last_bit - first_bit + 1) * vmem->block_size; + + ret = cb(vmem, arg, offset, size); + if (ret) { + break; + } + first_bit = find_next_bit(vmem->bitmap, vmem->bitmap_size, + last_bit + 2); + } + return ret; +} + /* * Adjust the memory section to cover the intersection with the given range. * @@ -938,6 +962,10 @@ static int virtio_mem_post_load(void *opaque, int version_id) RamDiscardListener *rdl; int ret; + if (vmem->prealloc && !vmem->early_migration) { + warn_report("Proper preallocation with migration requires a newer QEMU machine"); + } + /* * We started out with all memory discarded and our memory region is mapped * into an address space. Replay, now that we updated the bitmap. @@ -957,6 +985,64 @@ static int virtio_mem_post_load(void *opaque, int version_id) return virtio_mem_restore_unplugged(vmem); } +static int virtio_mem_prealloc_range_cb(const VirtIOMEM *vmem, void *arg, + uint64_t offset, uint64_t size) +{ + void *area = memory_region_get_ram_ptr(&vmem->memdev->mr) + offset; + int fd = memory_region_get_fd(&vmem->memdev->mr); + Error *local_err = NULL; + + qemu_prealloc_mem(fd, area, size, 1, NULL, &local_err); + if (local_err) { + error_report_err(local_err); + return -ENOMEM; + } + return 0; +} + +static int virtio_mem_post_load_early(void *opaque, int version_id) +{ + VirtIOMEM *vmem = VIRTIO_MEM(opaque); + RAMBlock *rb = vmem->memdev->mr.ram_block; + int ret; + + if (!vmem->prealloc) { + return 0; + } + + /* + * We restored the bitmap and verified that the basic properties + * match on source and destination, so we can go ahead and preallocate + * memory for all plugged memory blocks, before actual RAM migration starts + * touching this memory. + */ + ret = virtio_mem_for_each_plugged_range(vmem, NULL, + virtio_mem_prealloc_range_cb); + if (ret) { + return ret; + } + + /* + * This is tricky: postcopy wants to start with a clean slate. On + * POSTCOPY_INCOMING_ADVISE, postcopy code discards all (ordinarily + * preallocated) RAM such that postcopy will work as expected later. + * + * However, we run after POSTCOPY_INCOMING_ADVISE -- but before actual + * RAM migration. So let's discard all memory again. This looks like an + * expensive NOP, but actually serves a purpose: we made sure that we + * were able to allocate all required backend memory once. We cannot + * guarantee that the backend memory we will free will remain free + * until we need it during postcopy, but at least we can catch the + * obvious setup issues this way. + */ + if (migration_incoming_postcopy_advised()) { + if (ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb))) { + return -EBUSY; + } + } + return 0; +} + typedef struct VirtIOMEMMigSanityChecks { VirtIOMEM *parent; uint64_t addr; @@ -1068,6 +1154,7 @@ static const VMStateDescription vmstate_virtio_mem_device_early = { .minimum_version_id = 1, .version_id = 1, .immutable = 1, + .post_load = virtio_mem_post_load_early, .fields = (VMStateField[]) { VMSTATE_WITH_TMP(VirtIOMEM, VirtIOMEMMigSanityChecks, vmstate_virtio_mem_sanity_checks),