Re: [Qemu-devel] [PATCH 2/2] cpu_physical_memory_write_rom() needs to do TB invalidates

[Anthony Liguori]

Pavel Hrdina <address@hidden> writes:

> On 09/12/2012 07:57 AM, David Gibson wrote:
>> On Mon, Sep 10, 2012 at 03:27:45PM +0200, Andreas Färber wrote:
>>> Am 10.09.2012 04:30, schrieb David Gibson:
>>>> cpu_physical_memory_write_rom(), despite the name, can also be used to
>>>> write images into RAM - and will often be used that way if the machine
>>>> uses load_image_targphys() into RAM addresses.
>>>>
>>>> However, cpu_physical_memory_write_rom(), unlike cpu_physical_memory_rw()
>>>> does invalidate any cached TBs which might be affected by the region
>>> "doesn't"?
>>>
>>> Otherwise doesn't look wrong.
>> Oops, comment updated.
>>
>>  From 6b913afaf83f52ee787271827c84b492e8ac5895 Mon Sep 17 00:00:00 2001
>> From: David Gibson <address@hidden>
>> Date: Wed, 22 Aug 2012 14:58:04 +1000
>> Subject: [PATCH] cpu_physical_memory_write_rom() needs to do TB invalidates
>>
>> cpu_physical_memory_write_rom(), despite the name, can also be used to
>> write images into RAM - and will often be used that way if the machine
>> uses load_image_targphys() into RAM addresses.
>>
>> However, cpu_physical_memory_write_rom(), unlike
>> cpu_physical_memory_rw() doesn't invalidate any cached TBs which might
>> be affected by the region written.
>>
>> This was breaking reset (under full emu) on the pseries machine - we loaded
>> our firmware image into RAM, and while executing it rewrite the code at
>> the entry point (correctly causing a TB invalidate/refresh).  When we
>> reset the firmware image was reloaded, but the TB from the rewrite was
>> still active and caused us to get an illegal instruction trap.
>>
>> This patch fixes the bug by duplicating the tb invalidate code from
>> cpu_physical_memory_rw() in cpu_physical_memory_write_rom().
>>
>> Signed-off-by: David Gibson <address@hidden>
>> ---
>>   exec.c |    7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/exec.c b/exec.c
>> index 5834766..eff40d7 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -3523,6 +3523,13 @@ void cpu_physical_memory_write_rom(target_phys_addr_t 
>> addr,
>>               /* ROM/RAM case */
>>               ptr = qemu_get_ram_ptr(addr1);
>>               memcpy(ptr, buf, l);
>> +            if (!cpu_physical_memory_is_dirty(addr1)) {
>> +                /* invalidate code */
>> +                tb_invalidate_phys_page_range(addr1, addr1 + l, 0);
>> +                /* set dirty bit */
>> +                cpu_physical_memory_set_dirty_flags(
>> +                    addr1, (0xff & ~CODE_DIRTY_FLAG));
>> +            }
>>               qemu_put_ram_ptr(ptr);
>>           }
>>           len -= l;
> Hi,
>
> this patch breaks Windows XP guest at all. Windows XP boot ends in loob 
> by restarting itself after time-out expires in windows advanced boot 
> options.
>
> I started the guest using this command-line:
>
> ./x86_64-softmmu/qemu-system-x86_64 -m 2G -drive 
> file=/data/data-shared/images/winxp-test.img -vnc 0.0.0.0:0

Does changing the tb_invalidate_phys_page_range() call to:

tb_invalidate_phys_page_range(addr1, addr1 + MAX(l, TARGET_PAGE_SIZE), 0);

The dirty flag is being reset for the full page but we're potentially
only invalidating a subset of TBs that occur on the page.

Regards,

Anthony Liguori


>
> Pavel