Re: [Qemu-devel] [PATCH] isapc: Shadow ISA BIOS by default

[Anthony Liguori <aliguori@us.ibm.com>]

Jan Kiszka <jan.kiszka@siemens.com> writes:

> On 2012-10-08 20:52, Anthony Liguori wrote:
>> Jan Kiszka <jan.kiszka@siemens.com> writes:
>> 
>>> On 2012-09-11 17:53, Jan Kiszka wrote:
>>>> Our one and only BIOS depends on a writable shadowed BIOS in the ISA
>>>> range. As we have no interface to control the write property, make that
>>>> region writable by default.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>> ---
>>>>
>>>> This unbreaks isapc for TCG, and keep it working for KVM once it starts
>>>> supporting read-only memslots.
>>>>
>>>>  hw/pc_sysfw.c |   13 +++++++++----
>>>>  1 files changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/hw/pc_sysfw.c b/hw/pc_sysfw.c
>>>> index b45f0ac..027d98a 100644
>>>> --- a/hw/pc_sysfw.c
>>>> +++ b/hw/pc_sysfw.c
>>>> @@ -136,6 +136,7 @@ static void old_pc_system_rom_init(MemoryRegion *rom_memory)
>>>>  {
>>>>      char *filename;
>>>>      MemoryRegion *bios, *isa_bios;
>>>> +    void *isa_bios_ptr;
>>>>      int bios_size, isa_bios_size;
>>>>      int ret;
>>>>  
>>>> @@ -167,19 +168,23 @@ static void old_pc_system_rom_init(MemoryRegion *rom_memory)
>>>>          g_free(filename);
>>>>      }
>>>>  
>>>> -    /* map the last 128KB of the BIOS in ISA space */
>>>> +    /* Shadow the last 128KB of the BIOS in ISA space as RAM -
>>>> +     * Seabios depends on this */
>>>>      isa_bios_size = bios_size;
>>>>      if (isa_bios_size > (128 * 1024)) {
>>>>          isa_bios_size = 128 * 1024;
>>>>      }
>>>>      isa_bios = g_malloc(sizeof(*isa_bios));
>>>> -    memory_region_init_alias(isa_bios, "isa-bios", bios,
>>>> -                             bios_size - isa_bios_size, isa_bios_size);
>>>> +    memory_region_init_ram(isa_bios, "isa-bios", isa_bios_size);
>>>> +    vmstate_register_ram_global(isa_bios);
>>>>      memory_region_add_subregion_overlap(rom_memory,
>>>>                                          0x100000 - isa_bios_size,
>>>>                                          isa_bios,
>>>>                                          1);
>>>> -    memory_region_set_readonly(isa_bios, true);
>>>> +
>>>> +    /* copy ISA rom image from top of the ROM */
>>>> +    isa_bios_ptr = memory_region_get_ram_ptr(isa_bios);
>>>> +    rom_copy(isa_bios_ptr, (uint32_t)(-isa_bios_size), isa_bios_size);
>>>>  
>>>>      /* map all the bios at the top of memory */
>>>>      memory_region_add_subregion(rom_memory,
>>>>
>>>
>>> Ping. Or already queued?
>> 
>> I've got it queued now.  Thanks.
>
> I'm withdrawing it: This breaks Windows 95 booting. For unknown reasons,
> this nice OS decided to overwrite the F-segment during boot. That is
> fine as long as it is properly protected. But it breaks under current
> KVM and with the patch above for the isapc. So we need a firmware
> interface to enable/disable write protection for this segment in isapc
> mode, specifically as that machine targets these old OSes.

Ah, if it wasn't for a build break caused by one of the pull requests, I
would have pushed last night.  Thanks for the heads up, I'll remove it
from my queue.

Is fw_cfg the right interface?  I presume this is i440fx specific?  How
does q35 handle this?  Presumably there's a second window for the BIOS
mapping.  There's got to be some way to do shadowing of it I would
think.

Regards,

Anthony Liguori

>
> Jan
>
> -- 
> Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
> Corporate Competence Center Embedded Linux