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

[Andrew Jones <drjones@redhat.com>]

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;
 }
 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 {
-- 
2.25.4