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

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

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

>
> Pavel
>
>>> Pavel