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[79.180.10.140]) by smtp.gmail.com with ESMTPSA id n16sm3306725wmc.40.2020.07.14.02.31.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2020 02:31:46 -0700 (PDT) Date: Tue, 14 Jul 2020 05:31:43 -0400 From: "Michael S. Tsirkin" To: Andrew Jones Subject: Re: [PATCH 3/4] hw/arm/virt-acpi-build: Only expose flash on older machine types Message-ID: <20200714053023-mutt-send-email-mst@kernel.org> References: <20200629140938.17566-1-drjones@redhat.com> <20200629140938.17566-4-drjones@redhat.com> <20200713104907.335bf762@redhat.com> <20200714055109.owrlob6m53notzh3@kamzik.brq.redhat.com> <20200714045537-mutt-send-email-mst@kernel.org> <20200714092325.5klaeqelu46mhg76@kamzik.brq.redhat.com> MIME-Version: 1.0 In-Reply-To: <20200714092325.5klaeqelu46mhg76@kamzik.brq.redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/14 03:57:32 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, eric.auger@redhat.com, philmd@redhat.com, qemu-devel@nongnu.org, shannon.zhaosl@gmail.com, qemu-arm@nongnu.org, ard.biesheuvel@arm.com, Igor Mammedov , lersek@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 14, 2020 at 11:23:25AM +0200, Andrew Jones wrote: > On Tue, Jul 14, 2020 at 04:57:50AM -0400, Michael S. Tsirkin wrote: > > On Tue, Jul 14, 2020 at 07:51:09AM +0200, Andrew Jones wrote: > > > On Mon, Jul 13, 2020 at 10:49:07AM +0200, Igor Mammedov wrote: > > > > On Mon, 29 Jun 2020 16:09:37 +0200 > > > > Andrew Jones wrote: > > > > > > > > > The flash device is exclusively for the host-controlled firmware, so > > > > > we should not expose it to the OS. Exposing it risks the OS messing > > > > > with it, which could break firmware runtime services and surprise the > > > > > OS when all its changes disappear after reboot. > > > > > > > > > > As firmware needs the device and uses DT, we leave the device exposed > > > > > there. It's up to firmware to remove the nodes from DT before sending > > > > > it on to the OS. However, there's no need to force firmware to remove > > > > > tables from ACPI (which it doesn't know how to do anyway), so we > > > > > simply don't add the tables in the first place. But, as we've been > > > > > adding the tables for quite some time and don't want to change the > > > > > default hardware exposed to versioned machines, then we only stop > > > > > exposing the flash device tables for 5.1 and later machine types. > > > > > > > > > > Suggested-by: Ard Biesheuvel > > > > > Suggested-by: Laszlo Ersek > > > > > Signed-off-by: Andrew Jones > > > > > --- > > > > > hw/arm/virt-acpi-build.c | 5 ++++- > > > > > hw/arm/virt.c | 3 +++ > > > > > include/hw/arm/virt.h | 1 + > > > > > 3 files changed, 8 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c > > > > > index 1384a2cf2ab4..91f0df7b13a3 100644 > > > > > --- a/hw/arm/virt-acpi-build.c > > > > > +++ b/hw/arm/virt-acpi-build.c > > > > > @@ -749,6 +749,7 @@ static void build_fadt_rev5(GArray *table_data, BIOSLinker *linker, > > > > > static void > > > > > build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) > > > > > { > > > > > + VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(vms); > > > > > Aml *scope, *dsdt; > > > > > MachineState *ms = MACHINE(vms); > > > > > const MemMapEntry *memmap = vms->memmap; > > > > > @@ -767,7 +768,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) > > > > > acpi_dsdt_add_cpus(scope, vms->smp_cpus); > > > > > acpi_dsdt_add_uart(scope, &memmap[VIRT_UART], > > > > > (irqmap[VIRT_UART] + ARM_SPI_BASE)); > > > > > - acpi_dsdt_add_flash(scope, &memmap[VIRT_FLASH]); > > > > > + if (vmc->acpi_expose_flash) { > > > > > + acpi_dsdt_add_flash(scope, &memmap[VIRT_FLASH]); > > > > > + } > > > > > acpi_dsdt_add_fw_cfg(scope, &memmap[VIRT_FW_CFG]); > > > > > acpi_dsdt_add_virtio(scope, &memmap[VIRT_MMIO], > > > > > (irqmap[VIRT_MMIO] + ARM_SPI_BASE), NUM_VIRTIO_TRANSPORTS); > > > > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c > > > > > index cd0834ce7faf..5adc9ff799ef 100644 > > > > > --- a/hw/arm/virt.c > > > > > +++ b/hw/arm/virt.c > > > > > @@ -2482,9 +2482,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(5, 1) > > > > > > > > > > static void virt_machine_5_0_options(MachineClass *mc) > > > > > { > > > > > + VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc)); > > > > > + > > > > > virt_machine_5_1_options(mc); > > > > > compat_props_add(mc->compat_props, hw_compat_5_0, hw_compat_5_0_len); > > > > > mc->numa_mem_supported = true; > > > > > + vmc->acpi_expose_flash = true; > > > > > > > > we usually do not version ACPI tables changes > > > > (unless we have a good reason to do so) > > > > > > Even when the change is to remove the exposure of hardware from the guest? > > > Before this change, if a guest looked, it had a flash, after this change, > > > if a guest looks, it doesn't. > > > > It's up to the relevant maintainers who know what the semantics are. > > FYI ACPI tables only change across a reset though. > > So it's a question of whether guests get confused even if this > > changes after a reboot. > > Yup, but it's still the same "machine", so a user may wonder why it > changed. > > > Versioning is generally safer, but it's a good idea to document > > the motivation for it. > > > > Well, in this case, we could probably push this change to old machine > types and nobody would notice. If a guest is using ACPI, then it must > be using firmware, and if they're using firmware, then they can't be > using the flash. So the user shouldn't care if it's there or not. The > only justification for the versioning is because "it's safer". If > people feel strongly about avoiding versioning when it's not obviously > necessary, then I can respin without it. > > Thanks, > drew It's up to maintainers either way, but please do tweak the motivation in the commit log to include the above. -- MST