[Qemu-devel] Re: sparc solaris guest, hsfs_putpage: dirty HSFS page

[Blue Swirl]

On Tue, Jan 26, 2010 at 10:42 PM, Artyom Tarasenko
<address@hidden> wrote:
> 2010/1/26 Blue Swirl <address@hidden>:
>> On Tue, Jan 26, 2010 at 7:03 PM, Artyom Tarasenko
>> <address@hidden> wrote:
>>> 2010/1/24 Blue Swirl <address@hidden>:
>>>> On Sun, Jan 24, 2010 at 2:02 AM, Artyom Tarasenko
>>>> <address@hidden> wrote:
>>>>> All solaris versions which currently boot (from cd) regularly produce 
>>>>> buckets of
>>>>> "hsfs_putpage: dirty HSFS page" messages.
>>>>>
>>>>> High Sierra is a pretty old and stable stuff, so it is possible that
>>>>> the code is similar to OpenSolaris.
>>>>> I looked in debugger, and the function calls hierarchy looks pretty 
>>>>> similar.
>>>>>
>>>>> Now in the OpenSolaris source code there is a nice comment:
>>>>> http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/hsfs/hsfs_vnops.c#1758
>>>>> /*
>>>>> * Normally pvn_getdirty() should return 0, which
>>>>> * impies that it has done the job for us.
>>>>> * The shouldn't-happen scenario is when it returns 1.
>>>>> * This means that the page has been modified and
>>>>> * needs to be put back.
>>>>> * Since we can't write on a CD, we fake a failed
>>>>> * I/O and force pvn_write_done() to destroy the page.
>>>>> */
>>>>> if (pvn_getdirty(pp, flags) == 1) {
>>>>>                cmn_err(CE_NOTE,
>>>>>                            "hsfs_putpage: dirty HSFS page");
>>>>>
>>>>> Now the question: does the problem have to do with qemu caches 
>>>>> (non-)emulation?
>>>>> Can it be that we mark non-dirty pages dirty? Or does qemu always mark
>>>>> pages dirty exactly to avoid cache emulation?
>>>>>
>>>>> Otherwise it means something else goes astray and Solaris guest really
>>>>> modifies the pages it shouldn't.
>>>>>
>>>>> Just wonder what to dig first, MMU or IRQ emulation (the two most
>>>>> obvious suspects).
>>>>
>>>> Maybe the stores via MMU bypass ASIs
>>>
>>> why bypass stores? What about the non-bypass ones?
>>
>> Because their use should update the PTE dirty bits.
>
> update !=always set. Where is it implemented? I guess the code is
> shared between multiple architectures.
> Is there a way to trace at what point certain page is getting dirty?
>
> Since it's not the bypass ASIs it must be something else.

target-sparc/helper.c:193 for the page table dirtiness (this is
probably what Solaris can detect).

There is other kind of dirtiness in exec.c, grep for phys_ram_dirty
uses. But this should not be visible to guest.