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 06:21 PM, Anthony Liguori wrote:
> Pavel Hrdina <phrdina@redhat.com> writes:
>
>> 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.
> Then I'm confused...  invalidating TBs should never have a functional
> impact IIUC.  Are you confident in your bisection?  Reverting this patch
> fixes the problem?
>
> Regards,
>
> Anthony Liguori

Yes I'm 100% sure that this commit cause this bug. I've tried to revert 
this patch and it works OK.

Pavel
>> Pavel
>>
>>>> Pavel
>