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

[Pavel Hrdina <phrdina@redhat.com>]

On 10/01/2012 04:28 PM, Anthony Liguori wrote:
> Pavel Hrdina <phrdina@redhat.com> 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 <david@gibson.dropbear.id.au>
>>> 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 <david@gibson.dropbear.id.au>
>>> ---
>>>    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
>

No, it doesn't fix this bug.

Pavel

>> Pavel