Re: [PATCH] hw/arm: add pvpanic mmio device for arm

[Igor Mammedov <imammedo@redhat.com>]

On Sat, 4 Oct 2025 23:19:09 +0300
Alexander Gryanko <xpahos@gmail.com> wrote:

> Currently, pvpanic is available in three device types: ISA,
> MMIO, and PCI. For early stages of system initialisation
> before PCI enumeration, only ISA and MMIO are suitable.
> ISA is specific to the x86 platform; only MMIO devices
> can be used for ARM. It is not possible to specify a
> device as on the x86 platform (-device pvpanic); the

perhaps ARM folsk know better, don't we have some
user create-able sysbus devices? Can it be implemented
as such, so we would avoid creating built-in device?

> only possible way is to add an MMIO device to the dtb,
> which can be implemented by manually adding new functions
> to the QEMU code, as was done in the VMApple implementation.
> 
> Signed-off-by: Alexander Gryanko <xpahos@gmail.com>
> ---
> hw/arm/virt.c         | 25 +++++++++++++++++++++++++
> include/hw/arm/virt.h |  1 +
> 2 files changed, 26 insertions(+)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 02209fadcf..1059584b67 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -39,6 +39,7 @@
> #include "hw/arm/virt.h"
> #include "hw/block/flash.h"
> #include "hw/display/ramfb.h"
> +#include "hw/misc/pvpanic.h"
> #include "net/net.h"
> #include "system/device_tree.h"
> #include "system/numa.h"
> @@ -182,6 +183,7 @@ static const MemMapEntry base_memmap[] = {
>     [VIRT_UART0] =              { 0x09000000, 0x00001000 },
>     [VIRT_RTC] =                { 0x09010000, 0x00001000 },
>     [VIRT_FW_CFG] =             { 0x09020000, 0x00000018 },
> +    [VIRT_PVPANIC] =            { 0x09021000, 0x00000002 },
>     [VIRT_GPIO] =               { 0x09030000, 0x00001000 },
>     [VIRT_UART1] =              { 0x09040000, 0x00001000 },
>     [VIRT_SMMU] =               { 0x09050000, SMMU_IO_LEN },
> @@ -276,6 +278,27 @@ static bool ns_el2_virt_timer_present(void)
>         arm_feature(env, ARM_FEATURE_EL2) && cpu_isar_feature(aa64_vh, cpu);
> }
> 
> +static void create_pvpanic(VirtMachineState *vms)
> +{
> +    char *nodename;
> +    MachineState *ms = MACHINE(vms);
> +    DeviceState *dev = qdev_new(TYPE_PVPANIC_MMIO_DEVICE);
> +    SysBusDevice *s = SYS_BUS_DEVICE(dev);
> +
> +    hwaddr base = vms->memmap[VIRT_PVPANIC].base;
> +    hwaddr size = vms->memmap[VIRT_PVPANIC].size;
> +
> +    sysbus_realize_and_unref(s, &error_fatal);
> +    sysbus_mmio_map(s, 0, base);
> +
> +    nodename = g_strdup_printf("/pvpanic@%" PRIx64, base);
> +    qemu_fdt_add_subnode(ms->fdt, nodename);
> +    qemu_fdt_setprop_string(ms->fdt, nodename, "compatible",
> +                            "qemu,pvpanic-mmio");
> +    qemu_fdt_setprop_sized_cells(ms->fdt, nodename, "reg",
> +                                 2, base, 2, size);
> +}
> +
> static void create_fdt(VirtMachineState *vms)
> {
>     MachineState *ms = MACHINE(vms);
> @@ -2498,6 +2521,8 @@ static void machvirt_init(MachineState *machine)
>     create_pcie(vms);
>     create_cxl_host_reg_region(vms);
> 
> +    create_pvpanic(vms);

given that virt is versioned machine type,
we probably need a compat knob to disable it's creation on old machine types

> +
>     if (has_ged && aarch64 && firmware_loaded && virt_is_acpi_enabled(vms)) {
>         vms->acpi_dev = create_acpi_ged(vms);
>     } else {
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index ea2cff05b0..39bf07c9c1 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -81,6 +81,7 @@ enum {
>     VIRT_NVDIMM_ACPI,
>     VIRT_PVTIME,
>     VIRT_ACPI_PCIHP,
> +    VIRT_PVPANIC,
>     VIRT_LOWMEMMAP_LAST,
> };
> 
> 
> ---
> base-commit: bd6aa0d1e59d71218c3eee055bc8d222c6e1a628
> change-id: 20251004-arm-pvpanic-84a7d7b67d8d
> 
> Best regards,