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


From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH] isapc: Shadow ISA BIOS by default
Date: Fri, 12 Oct 2012 11:29:47 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666

On 2012-10-08 20:52, Anthony Liguori wrote:
> Jan Kiszka <address@hidden> 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 <address@hidden>
>>> ---
>>>
>>> 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.

Jan

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



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