Re: [PATCH 3/4] hw/arm/virt-acpi-build: Only expose flash on older machine types

[Igor Mammedov]

On Mon, 29 Jun 2020 16:09:37 +0200
Andrew Jones <drjones@redhat.com> 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 <ard.biesheuvel@arm.com>
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  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)

>  }
>  DEFINE_VIRT_MACHINE(5, 0)
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 31878ddc7223..c65be5fe0bb6 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -119,6 +119,7 @@ typedef struct {
>      bool no_highmem_ecam;
>      bool no_ged;   /* Machines < 4.2 has no support for ACPI GED device */
>      bool kvm_no_adjvtime;
> +    bool acpi_expose_flash;
>  } VirtMachineClass;
>  
>  typedef struct {