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 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 EC296C46467 for ; Wed, 4 Jan 2023 12:15:06 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pD2ef-0002bd-RI; Wed, 04 Jan 2023 07:14:01 -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 1pD2ed-0002ab-W7 for qemu-devel@nongnu.org; Wed, 04 Jan 2023 07:14:00 -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 1pD2eb-0005KJ-S8 for qemu-devel@nongnu.org; Wed, 04 Jan 2023 07:13:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1672834436; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ApWHVRgr7ojdZmOlPtiuphY1qtafEMz8GZdE2L1wyZ8=; b=iw5+k4XfuXFkAqbeIsL7VLBrVYO0C0E5S5cUhwTPQHgO7J4KIkrWrmhSNSE0GoMfx6caUh Ip/pCUpqTTT/pK4FkYyG6XKZYh8e27oqb4RuvPC+90tRlMZA8GwyiCA9OqqQJaIpH4LKsW kvBY2XRZsDcnJOBuF6cqR4al4zOUjyI= 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-488-Uy28uKNVNWaiCgTj6zAz4Q-1; Wed, 04 Jan 2023 07:13:53 -0500 X-MC-Unique: Uy28uKNVNWaiCgTj6zAz4Q-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1B6892A5954A; Wed, 4 Jan 2023 12:13:53 +0000 (UTC) Received: from [10.39.192.86] (unknown [10.39.192.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A677A49BB6A; Wed, 4 Jan 2023 12:13:50 +0000 (UTC) Message-ID: Date: Wed, 4 Jan 2023 13:13:49 +0100 MIME-Version: 1.0 Subject: Re: [PATCH] acpi: cpuhp: fix guest-visible maximum access size to the legacy reg block Content-Language: en-US To: Igor Mammedov Cc: qemu devel list , "Michael S. Tsirkin" , Ani Sinha , Ard Biesheuvel , Paolo Bonzini , Peter Maydell , qemu-stable@nongnu.org References: <20230104090138.214862-1-lersek@redhat.com> <20230104113546.0f483ec4@imammedo.users.ipa.redhat.com> From: Laszlo Ersek In-Reply-To: <20230104113546.0f483ec4@imammedo.users.ipa.redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.133.124; envelope-from=lersek@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 On 1/4/23 11:35, Igor Mammedov wrote: > On Wed, 4 Jan 2023 10:01:38 +0100 > Laszlo Ersek wrote: > >> The modern ACPI CPU hotplug interface was introduced in the following >> series (aa1dd39ca307..679dd1a957df), released in v2.7.0: >> >> 1 abd49bc2ed2f docs: update ACPI CPU hotplug spec with new protocol >> 2 16bcab97eb9f pc: piix4/ich9: add 'cpu-hotplug-legacy' property >> 3 5e1b5d93887b acpi: cpuhp: add CPU devices AML with _STA method >> 4 ac35f13ba8f8 pc: acpi: introduce AcpiDeviceIfClass.madt_cpu hook >> 5 d2238cb6781d acpi: cpuhp: implement hot-add parts of CPU hotplug >> interface >> 6 8872c25a26cc acpi: cpuhp: implement hot-remove parts of CPU hotplug >> interface >> 7 76623d00ae57 acpi: cpuhp: add cpu._OST handling >> 8 679dd1a957df pc: use new CPU hotplug interface since 2.7 machine type >> >> Before patch#1, "docs/specs/acpi_cpu_hotplug.txt" only specified 1-byte >> accesses for the hotplug register block. Patch#1 preserved the same >> restriction for the legacy register block, but: >> >> - it specified DWORD accesses for some of the modern registers, >> >> - in particular, the switch from the legacy block to the modern block >> would require a DWORD write to the *legacy* block. >> >> The latter functionality was then implemented in cpu_status_write() >> [hw/acpi/cpu_hotplug.c], in patch#8. >> >> Unfortunately, all DWORD accesses depended on a dormant bug: the one >> introced in earlier commit a014ed07bd5a ("memory: accept mismatching sizes >> in memory_region_access_valid", 2013-05-29); first released in v1.6.0. >> Due to commit a014ed07bd5a, the DWORD accesses to the *legacy* CPU hotplug >> register block would work in spite of the above series *not* relaxing >> "valid.max_access_size = 1" in "hw/acpi/cpu_hotplug.c": >> >>> static const MemoryRegionOps AcpiCpuHotplug_ops = { >>> .read = cpu_status_read, >>> .write = cpu_status_write, >>> .endianness = DEVICE_LITTLE_ENDIAN, >>> .valid = { >>> .min_access_size = 1, >>> .max_access_size = 1, >>> }, >>> }; >> >> Later, in commits e6d0c3ce6895 ("acpi: cpuhp: introduce 'Command data 2' >> field", 2020-01-22) and ae340aa3d256 ("acpi: cpuhp: spec: add typical >> usecases", 2020-01-22), first released in v5.0.0, the modern CPU hotplug >> interface (including the documentation) was extended with another DWORD >> *read* access, namely to the "Command data 2" register, which would be >> important for the guest to confirm whether it managed to switch the >> register block from legacy to modern. >> >> This functionality too silently depended on the bug from commit >> a014ed07bd5a. >> >> In commit 5d971f9e6725 ('memory: Revert "memory: accept mismatching sizes >> in memory_region_access_valid"', 2020-06-26), first released in v5.1.0, >> the bug from commit a014ed07bd5a was fixed (the commit was reverted). >> That swiftly exposed the bug in "AcpiCpuHotplug_ops", still present from >> the v2.7.0 series quoted at the top -- namely the fact that >> "valid.max_access_size = 1" didn't match what the guest was supposed to >> do, according to the spec ("docs/specs/acpi_cpu_hotplug.txt"). >> >> The symptom is that the "modern interface negotiation protocol" >> described in commit ae340aa3d256: >> >>> + Use following steps to detect and enable modern CPU hotplug interface: >>> + 1. Store 0x0 to the 'CPU selector' register, >>> + attempting to switch to modern mode >>> + 2. Store 0x0 to the 'CPU selector' register, >>> + to ensure valid selector value >>> + 3. Store 0x0 to the 'Command field' register, >>> + 4. Read the 'Command data 2' register. >>> + If read value is 0x0, the modern interface is enabled. >>> + Otherwise legacy or no CPU hotplug interface available >> >> falls apart for the guest: steps 1 and 2 are lost, because they are DWORD >> writes; so no switching happens. Step 3 (a single-byte write) is not >> lost, but it has no effect; see the condition in cpu_status_write() in >> patch#8. And step 4 *misleads* the guest into thinking that the switch >> worked: the DWORD read is lost again -- it returns zero to the guest >> without ever reaching the device model, so the guest never learns the >> switch didn't work. >> >> This means that guest behavior centered on the "Command data 2" register >> worked *only* in the v5.0.0 release; it got effectively regressed in >> v5.1.0. >> >> To make things *even more* complicated, the breakage was (and remains, as >> of today) visible with TCG acceleration only. Commit 5d971f9e6725 makes >> no difference with KVM acceleration -- the DWORD accesses still work, >> despite "valid.max_access_size = 1". >> >> As commit 5d971f9e6725 suggests, fix the problem by raising >> "valid.max_access_size" to 4 -- the spec now clearly instructs the guest >> to perform DWORD accesses to the legacy register block too, for enabling >> (and verifying!) the modern block. In order to keep compatibility for the >> device model implementation though, set "impl.max_access_size = 1", so >> that wide accesses be split before they reach the legacy read/write >> handlers, like they always have been on KVM, and like they were on TCG >> before 5d971f9e6725 (v5.1.0). >> >> Tested with: >> >> - OVMF IA32 + qemu-system-i386, CPU hotplug/hot-unplug with SMM, >> intermixed with ACPI S3 suspend/resume, using KVM accel >> (regression-test); >> >> - OVMF IA32X64 + qemu-system-x86_64, CPU hotplug/hot-unplug with SMM, >> intermixed with ACPI S3 suspend/resume, using KVM accel >> (regression-test); >> >> - OVMF IA32 + qemu-system-i386, SMM enabled, using TCG accel; verified the >> register block switch and the present/possible CPU counting through the >> modern hotplug interface, during OVMF boot (bugfix test); > > >> - I do not have any testcase (guest payload) for regression-testing CPU >> hotplug through the *legacy* CPU hotplug register block. > I've checked it with old Seabios (that had it's own ACPI tables) (taken from 1.6 QEMU branch), > it works fine in TCG and KVM mode. > > Tested-by: Igor Mammedov Awesome, thank you! Laszlo > >> >> Cc: "Michael S. Tsirkin" >> Cc: Ani Sinha >> Cc: Ard Biesheuvel >> Cc: Igor Mammedov >> Cc: Paolo Bonzini >> Cc: Peter Maydell >> Cc: qemu-stable@nongnu.org >> Ref: "IO port write width clamping differs between TCG and KVM" >> Link: http://mid.mail-archive.com/aaedee84-d3ed-a4f9-21e7-d221a28d1683@redhat.com >> Link: https://lists.gnu.org/archive/html/qemu-devel/2023-01/msg00199.html >> Reported-by: Ard Biesheuvel >> Signed-off-by: Laszlo Ersek >> --- >> >> Notes: >> This should be applied to: >> >> - stable-5.2 (new branch) >> >> - stable-6.2 (new branch) >> >> - stable-7.2 (new branch) >> >> whichever is still considered maintained, as there is currently *no* >> public QEMU release in which the modern CPU hotplug register block >> works, when using TCG acceleration. v5.0.0 works, but that minor >> release has been obsoleted by v5.2.0, which does not work. >> >> hw/acpi/cpu_hotplug.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/hw/acpi/cpu_hotplug.c b/hw/acpi/cpu_hotplug.c >> index 53654f863830..ff14c3f4106f 100644 >> --- a/hw/acpi/cpu_hotplug.c >> +++ b/hw/acpi/cpu_hotplug.c >> @@ -52,6 +52,9 @@ static const MemoryRegionOps AcpiCpuHotplug_ops = { >> .endianness = DEVICE_LITTLE_ENDIAN, >> .valid = { >> .min_access_size = 1, >> + .max_access_size = 4, >> + }, >> + .impl = { >> .max_access_size = 1, >> }, >> }; >