Re: [PATCH v3 6/6] hw/i386/pc_sysfw: Alias rather than copy isa-bios region

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 08, 2024 at 07:55:07PM +0200, Bernhard Beschow wrote:
> In the -bios case the "isa-bios" memory region is an alias to the BIOS mapped
> to the top of the 4G memory boundary. Do the same in the -pflash case, but only
> for new machine versions for migration compatibility. This establishes common
> behavior and makes pflash commands work in the "isa-bios" region which some
> real-world legacy bioses rely on.
> 
> Note that in the sev_enabled() case, the "isa-bios" memory region in the -pflash
> case will now also point to encrypted memory, just like it already does in the
> -bios case.
> 
> When running `info mtree` before and after this commit with
> `qemu-system-x86_64 -S -drive \
> if=pflash,format=raw,readonly=on,file=/usr/share/qemu/bios-256k.bin` and running
> `diff -u before.mtree after.mtree` results in the following changes in the
> memory tree:
> 
>    --- before.mtree
>    +++ after.mtree
>    @@ -71,7 +71,7 @@
>         0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>         00000000000a0000-00000000000bffff (prio 1, i/o): vga-lowmem
>         00000000000c0000-00000000000dffff (prio 1, rom): pc.rom
>    -      00000000000e0000-00000000000fffff (prio 1, rom): isa-bios
>    +      00000000000e0000-00000000000fffff (prio 1, romd): alias isa-bios @system.flash0 0000000000020000-000000000003ffff
>         00000000000a0000-00000000000bffff (prio 1, i/o): alias smram-region @pci 00000000000a0000-00000000000bffff
>         00000000000c0000-00000000000c3fff (prio 1, i/o): alias pam-pci @pci 00000000000c0000-00000000000c3fff
>         00000000000c4000-00000000000c7fff (prio 1, i/o): alias pam-pci @pci 00000000000c4000-00000000000c7fff
>    @@ -108,7 +108,7 @@
>         0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>         00000000000a0000-00000000000bffff (prio 1, i/o): vga-lowmem
>         00000000000c0000-00000000000dffff (prio 1, rom): pc.rom
>    -      00000000000e0000-00000000000fffff (prio 1, rom): isa-bios
>    +      00000000000e0000-00000000000fffff (prio 1, romd): alias isa-bios @system.flash0 0000000000020000-000000000003ffff
>         00000000000a0000-00000000000bffff (prio 1, i/o): alias smram-region @pci 00000000000a0000-00000000000bffff
>         00000000000c0000-00000000000c3fff (prio 1, i/o): alias pam-pci @pci 00000000000c0000-00000000000c3fff
>         00000000000c4000-00000000000c7fff (prio 1, i/o): alias pam-pci @pci 00000000000c4000-00000000000c7fff
>    @@ -131,11 +131,14 @@
>    memory-region: pc.ram
>    0000000000000000-0000000007ffffff (prio 0, ram): pc.ram
> 
>    +memory-region: system.flash0
>    +  00000000fffc0000-00000000ffffffff (prio 0, romd): system.flash0
>    +
>    memory-region: pci
>    0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>         00000000000a0000-00000000000bffff (prio 1, i/o): vga-lowmem
>         00000000000c0000-00000000000dffff (prio 1, rom): pc.rom
>    -    00000000000e0000-00000000000fffff (prio 1, rom): isa-bios
>    +    00000000000e0000-00000000000fffff (prio 1, romd): alias isa-bios @system.flash0 0000000000020000-000000000003ffff
> 
>    memory-region: smram
>         00000000000a0000-00000000000bffff (prio 0, ram): alias smram-low @pc.ram 00000000000a0000-00000000000bffff
> 
> Note that in both cases the "system" memory region contains the entry
> 
>   00000000fffc0000-00000000ffffffff (prio 0, romd): system.flash0
> 
> but the "system.flash0" memory region only appears standalone when "isa-bios" is
> an alias.
> 
> Signed-off-by: Bernhard Beschow <shentey@gmail.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

feel free to queue

> ---
>  include/hw/i386/pc.h | 1 +
>  hw/i386/pc.c         | 1 +
>  hw/i386/pc_piix.c    | 3 +++
>  hw/i386/pc_q35.c     | 2 ++
>  hw/i386/pc_sysfw.c   | 8 +++++++-
>  5 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index e52290916c..ad9c3d9ba8 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -119,6 +119,7 @@ struct PCMachineClass {
>      bool enforce_aligned_dimm;
>      bool broken_reserved_end;
>      bool enforce_amd_1tb_hole;
> +    bool isa_bios_alias;
>  
>      /* generate legacy CPU hotplug AML */
>      bool legacy_cpu_hotplug;
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 46235466d7..4878705af7 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1812,6 +1812,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
>      pcmc->has_reserved_memory = true;
>      pcmc->enforce_aligned_dimm = true;
>      pcmc->enforce_amd_1tb_hole = true;
> +    pcmc->isa_bios_alias = true;
>      /* BIOS ACPI tables: 128K. Other BIOS datastructures: less than 4K reported
>       * to be used at the moment, 32K should be enough for a while.  */
>      pcmc->acpi_data_size = 0x20000 + 0x8000;
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index 8850c49c66..d4e9deb509 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -525,12 +525,15 @@ DEFINE_I440FX_MACHINE(v9_1, "pc-i440fx-9.1", NULL,
>  
>  static void pc_i440fx_9_0_machine_options(MachineClass *m)
>  {
> +    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> +
>      pc_i440fx_9_1_machine_options(m);
>      m->alias = NULL;
>      m->is_default = false;
>  
>      compat_props_add(m->compat_props, hw_compat_9_0, hw_compat_9_0_len);
>      compat_props_add(m->compat_props, pc_compat_9_0, pc_compat_9_0_len);
> +    pcmc->isa_bios_alias = false;
>  }
>  
>  DEFINE_I440FX_MACHINE(v9_0, "pc-i440fx-9.0", NULL,
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index bb53a51ac1..bd7db4abac 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -378,10 +378,12 @@ DEFINE_Q35_MACHINE(v9_1, "pc-q35-9.1", NULL,
>  
>  static void pc_q35_9_0_machine_options(MachineClass *m)
>  {
> +    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
>      pc_q35_9_1_machine_options(m);
>      m->alias = NULL;
>      compat_props_add(m->compat_props, hw_compat_9_0, hw_compat_9_0_len);
>      compat_props_add(m->compat_props, pc_compat_9_0, pc_compat_9_0_len);
> +    pcmc->isa_bios_alias = false;
>  }
>  
>  DEFINE_Q35_MACHINE(v9_0, "pc-q35-9.0", NULL,
> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
> index 82d37cb376..ac88ad4eb9 100644
> --- a/hw/i386/pc_sysfw.c
> +++ b/hw/i386/pc_sysfw.c
> @@ -135,6 +135,7 @@ static void pc_system_flash_map(PCMachineState *pcms,
>                                  MemoryRegion *rom_memory)
>  {
>      X86MachineState *x86ms = X86_MACHINE(pcms);
> +    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>      hwaddr total_size = 0;
>      int i;
>      BlockBackend *blk;
> @@ -184,7 +185,12 @@ static void pc_system_flash_map(PCMachineState *pcms,
>  
>          if (i == 0) {
>              flash_mem = pflash_cfi01_get_memory(system_flash);
> -            pc_isa_bios_init(&x86ms->isa_bios, rom_memory, flash_mem);
> +            if (pcmc->isa_bios_alias) {
> +                x86_isa_bios_init(&x86ms->isa_bios, rom_memory, flash_mem,
> +                                  true);
> +            } else {
> +                pc_isa_bios_init(&x86ms->isa_bios, rom_memory, flash_mem);
> +            }
>  
>              /* Encrypt the pflash boot ROM */
>              if (sev_enabled()) {
> -- 
> 2.45.0