[Qemu-devel] Re: [PATCH 1/2] Pad iommu with an empty slot (necessary for SunOS 4.1.4)

[Artyom Tarasenko <atar4qemu@googlemail.com>]

2010/5/21 Blue Swirl <blauwirbel@gmail.com>:
> On Fri, May 21, 2010 at 5:23 PM, Artyom Tarasenko
> <atar4qemu@googlemail.com> wrote:
>> 2010/5/10 Blue Swirl <blauwirbel@gmail.com>:
>>> On 5/10/10, Artyom Tarasenko <atar4qemu@googlemail.com> wrote:
>>>> 2010/5/10 Blue Swirl <blauwirbel@gmail.com>:
>>>>
>>>> > On 5/10/10, Artyom Tarasenko <atar4qemu@googlemail.com> wrote:
>>>>  >> 2010/5/9 Blue Swirl <blauwirbel@gmail.com>:
>>>>  >>  > On 5/9/10, Artyom Tarasenko <atar4qemu@googlemail.com> wrote:
>>>>  >>  >> 2010/5/9 Blue Swirl <blauwirbel@gmail.com>:
>>>>  >>  >>
>>>>  >>  >> > On 5/8/10, Artyom Tarasenko <atar4qemu@googlemail.com> wrote:
>>>>  >>  >>  >> On the real hardware (SS-5, LX) the MMU is not padded, but aliased.
>>>>  >>  >>  >>  Software shouldn't use aliased addresses, neither should it crash
>>>>  >>  >>  >>  when it uses (on the real hardware it wouldn't). Using empty_slot
>>>>  >>  >>  >>  instead of aliasing can help with debugging such accesses.
>>>>  >>  >>  >
>>>>  >>  >>  > TurboSPARC Microprocessor User's Manual shows that there are
>>>>  >>  >>  > additional pages after the main IOMMU for AFX registers. So this is
>>>>  >>  >>  > not board specific, but depends on CPU/IOMMU versions.
>>>>  >>  >>
>>>>  >>  >>
>>>>  >>  >> I checked it on the real hw: on LX and SS-5 these are aliased MMU addresses.
>>>>  >>  >>  SS-20 doesn't have any aliasing.
>>>>  >>  >
>>>>  >>  > But are your machines equipped with TurboSPARC or some other CPU?
>>>>  >>
>>>>  >>
>>>>  >> Good point, I must confess, I missed the word "Turbo" in your first
>>>>  >>  answer. LX and SS-20 don't.
>>>>  >>  But SS-5 must have a TurboSPARC CPU:
>>>>  >>
>>>>  >>  ok cd /FMI,MB86904
>>>>  >>  ok .attributes
>>>>  >>  context-table            00 00 00 00 03 ff f0 00 00 00 10 00
>>>>  >>  psr-implementation       00000000
>>>>  >>  psr-version              00000004
>>>>  >>  implementation           00000000
>>>>  >>  version                  00000004
>>>>  >>  cache-line-size          00000020
>>>>  >>  cache-nlines             00000200
>>>>  >>  page-size                00001000
>>>>  >>  dcache-line-size         00000010
>>>>  >>  dcache-nlines            00000200
>>>>  >>  dcache-associativity     00000001
>>>>  >>  icache-line-size         00000020
>>>>  >>  icache-nlines            00000200
>>>>  >>  icache-associativity     00000001
>>>>  >>  ncaches                  00000002
>>>>  >>  mmu-nctx                 00000100
>>>>  >>  sparc-version            00000008
>>>>  >>  mask_rev                 00000026
>>>>  >>  device_type              cpu
>>>>  >>  name                     FMI,MB86904
>>>>  >>
>>>>  >>  and still it behaves the same as TI,TMS390S10 from the LX. This is done on SS-5:
>>>>  >>
>>>>  >>  ok 10000000 20 spacel@ .
>>>>  >>  4000009
>>>>  >>  ok 14000000 20 spacel@ .
>>>>  >>  4000009
>>>>  >>  ok 14000004 20 spacel@ .
>>>>  >>  23000
>>>>  >>  ok 1f000004 20 spacel@ .
>>>>  >>  23000
>>>>  >>  ok 10000008 20 spacel@ .
>>>>  >>  4000009
>>>>  >>  ok 14000028 20 spacel@ .
>>>>  >>  4000009
>>>>  >>  ok 1000000c 20 spacel@ .
>>>>  >>  23000
>>>>  >>  ok 10000010 20 spacel@ .
>>>>  >>  4000009
>>>>  >>
>>>>  >>
>>>>  >>  LX is the same except for the IOMMU-version:
>>>>  >>
>>>>  >>  ok 10000000 20 spacel@ .
>>>>  >>  4000005
>>>>  >>  ok 14000000 20 spacel@ .
>>>>  >>  4000005
>>>>  >>  ok 18000000 20 spacel@ .
>>>>  >>  4000005
>>>>  >>  ok 1f000000 20 spacel@ .
>>>>  >>  4000005
>>>>  >>  ok 1ff00000 20 spacel@ .
>>>>  >>  4000005
>>>>  >>  ok 1fff0004 20 spacel@ .
>>>>  >>  1fe000
>>>>  >>  ok 10000004 20 spacel@ .
>>>>  >>  1fe000
>>>>  >>  ok 10000108 20 spacel@ .
>>>>  >>  41000005
>>>>  >>  ok 10000040 20 spacel@ .
>>>>  >>  41000005
>>>>  >>  ok 1fff0040 20 spacel@ .
>>>>  >>  41000005
>>>>  >>  ok 1fff0044 20 spacel@ .
>>>>  >>  1fe000
>>>>  >>  ok 1fff0024 20 spacel@ .
>>>>  >>  1fe000
>>>>  >>
>>>>  >>
>>>>  >>  >>  At what address the additional AFX registers are located?
>>>>  >>  >
>>>>  >>  > Here's complete TurboSPARC IOMMU address map:
>>>>  >>  >  PA[30:0]          Register          Access
>>>>  >>  > 1000_0000       IOMMU Control         R/W
>>>>  >>  > 1000_0004    IOMMU Base Address       R/W
>>>>  >>  > 1000_0014   Flush All IOTLB Entries    W
>>>>  >>  > 1000_0018        Address Flush         W
>>>>  >>  > 1000_1000  Asynchronous Fault Status  R/W
>>>>  >>  > 1000_1004 Asynchronous Fault Address  R/W
>>>>  >>  > 1000_1010  SBus Slot Configuration 0   R/W
>>>>  >>  > 1000_1014  SBus Slot Configuration 1   R/W
>>>>  >>  > 1000_1018  SBus Slot Configuration 2   R/W
>>>>  >>  > 1000_101C  SBus Slot Configuration 3   R/W
>>>>  >>  > 1000_1020  SBus Slot Configuration 4   R/W
>>>>  >>  > 1000_1050     Memory Fault Status     R/W
>>>>  >>  > 1000_1054    Memory Fault Address     R/W
>>>>  >>  > 1000_2000     Module Identification    R/W
>>>>  >>  > 1000_3018      Mask Identification      R
>>>>  >>  > 1000_4000      AFX Queue Level         W
>>>>  >>  > 1000_6000      AFX Queue Level         R
>>>>  >>  > 1000_7000      AFX Queue Status        R
>>>>  >>
>>>>  >>
>>>>  >>
>>>>  >> But if I read it correctly 0x12fff294 (which makes SunOS crash with -m 32) is
>>>>  >>  well above this limit.
>>>>  >
>>>>  > Oh, so I also misread something. You are not talking about the
>>>>  > adjacent pages, but 16MB increments.
>>>>  >
>>>>  > Earlier I sent a patch for a generic address alias device, would it be
>>>>  > useful for this?
>>>>
>>>>
>>>> Should do as well. But I thought empty_slot is less overhead and
>>>>  easier to debug.
>>>>
>>
>> Also the aliasing patch would require one more parameter: the size of
>> area which has to be aliased. Except we implement stubs for all
>> missing devices and and do aliasing of the connected port ranges. And
>> then again, SS-20 doesn't have aliasing in this area at all.
>>
>> What do you think about this (empty_slot) solution (except that I
>> missed the SoB line)? Meanwhile it's tested with SunOS 4.1.3U1 too.
>
> I'm slightly against it, of course it would help for this but I think
> we may be missing a bigger problem.
>
>>>>> Maybe we have a general design problem, perhaps unassigned access
>>>>> faults should only be triggered inside SBus slots and ignored
>>>>> elsewhere. If this is true, generic Sparc32 unassigned access handler
>>>>> should just ignore the access and special fault generating slots
>>>>> should be installed for empty SBus address ranges.
>>
>> Agreed that they should be special for SBus, because SS-20 OBP is
>> not happy with the fault we are currently generating. But otherwise I think qemu
>> does it correct. On SS-5:
>>
>> ok f7ff0000 2f spacel@ .
>> Data Access Error
>> ok sfar@ .
>> f7ff0000
>> ok 20000000 2f spacel@ .
>> Data Access Error
>> ok sfar@ .
>> 20000000
>> ok 40000000 20 spacel@ .
>> Data Access Error
>> ok sfar@ .
>> 40000000
>>
>> Neither ff7ff0000 nor f20000000, nor 40000000 are in SBus range,  right?
>
> 40000000 is on SS-5.

Ah. I was only aware of the control space. What ranges does SBus take?

> So is the SBus Control Space in 0x10000000 to
> 0x1fffffff the only area besides DRAM where the accesses won't trap?

At least some area after ROM is aliased too. Also on SS-10 with a
non-active frame buffer
writing to SX registers makes no visible effect and reading from them
produces no fault but a NMI.

>>>> My impression was that SS-5 and SS-20 do unassigned accesses a bit differently.
>>>>  The current IOMMU implementation fits SS-20, which has no aliasing.
>>>
>>> It's probably rather the board design than just IOMMU.
>>
>> Agreed. That's why I bound the patch to machine hwdef  and not to iommu.
>>
>>>>  >>  >>  > One approach would be that IOMMU_NREGS would be increased to cover
>>>>  >>  >>  > these registers (with the bump in savevm version field) and
>>>>  >>  >>  > iommu_init1() should check the version field to see how much MMIO to
>>>>  >>  >>  > provide.
>>>>  >>  >>
>>>>  >>  >>
>>>>  >>  >> The problem I see here is that we already have too much registers: we
>>>>  >>  >>  emulate SS-20 IOMMU (I guess), while SS-5 and LX seem to have only
>>>>  >>  >>  0x20 registers which are aliased all the way.
>>>>  >>  >>
>>>>  >>  >>
>>>>  >>  >>  > But in order to avoid the savevm version change, iommu_init1() could
>>>>  >>  >>  > just install dummy MMIO (in the TurboSPARC case), if OBP does not care
>>>>  >>  >>  > if the read back data matches what has been written earlier. Because
>>>>  >>  >>  > from OBP point of view this is identical to what your patch results
>>>>  >>  >>  > in, I'd suppose this approach would also work.
>>>>  >>  >>
>>>>  >>  >>
>>>>  >>  >> OBP doesn't seem to care about these addresses at all. It's only the "MUNIX"
>>>>  >>  >>  SunOS 4.1.4 kernel who does. The "MUNIX" kernel is the only kernel available
>>>>  >>  >>  during the installation, so it is currently not possible to install 4.1.4.
>>>>  >>  >>  Surprisingly "GENERIC" kernel which is on the disk after the
>>>>  >>  >>  installation doesn't
>>>>  >>  >>  try to access these address ranges either, so a disk image taken from a live
>>>>  >>  >>  system works.
>>>>  >>  >>
>>>>  >>  >>  Actually access to the non-connected/aliased addresses may also be a
>>>>  >>  >>  consequence of phys_page_find bug I mentioned before. When I run
>>>>  >>  >>  install with -m 64 and -m 256 it tries to access different
>>>>  >>  >>  non-connected addresses. May also be a SunOS bug of course. 256m used
>>>>  >>  >>  to be a lot back then.
>>>>  >>  >
>>>>  >>  > Perhaps with 256MB, memory probing advances blindly from memory to
>>>>  >>  > IOMMU registers. Proll (used before OpenBIOS) did that once, with bad
>>>>  >>  > results :-). If this is true, 64M, 128M and 192M should show identical
>>>>  >>  > results and only with close or equal to 256M the accesses happen.
>>>>  >>
>>>>  >>
>>>>  >> 32m: 0x12fff294
>>>>  >>  64m: 0x14fff294
>>>>  >>  192m:0x1cfff294
>>>>  >>  256m:0x20fff294
>>>>  >>
>>>>  >>  Memory probing? It would be strange that OS would do it itself. The OS
>>>>  >>  could just
>>>>  >>  ask OBP how much does it have. Here is the listing where it happens:
>>>>  >>
>>>>  >>  _swift_vac_rgnflush:            rd      %psr, %g2
>>>>  >>  _swift_vac_rgnflush+4:          andn    %g2, 0x20, %g5
>>>>  >>  _swift_vac_rgnflush+8:          mov     %g5, %psr
>>>>  >>  _swift_vac_rgnflush+0xc:        nop
>>>>  >>  _swift_vac_rgnflush+0x10:       nop
>>>>  >>  _swift_vac_rgnflush+0x14:       mov     0x100, %g5
>>>>  >>  _swift_vac_rgnflush+0x18:       lda     [%g5] 0x4, %g5
>>>>  >>  _swift_vac_rgnflush+0x1c:       sll     %o2, 0x2, %g1
>>>>  >>  _swift_vac_rgnflush+0x20:       sll     %g5, 0x4, %g5
>>>>  >>  _swift_vac_rgnflush+0x24:       add     %g5, %g1, %g5
>>>>  >>  _swift_vac_rgnflush+0x28:       lda     [%g5] 0x20, %g5
>>>>  >>
>>>>  >>  _swift_vac_rgnflush+0x28: is the fatal one.
>>>>  >>
>>>>  >>  kadb> $c
>>>>  >>  _swift_vac_rgnflush(?)
>>>>  >>  _vac_rgnflush() + 4
>>>>  >>  _hat_setup_kas(0xc00,0xf0447000,0x43a000,0x400,0xf043a000,0x3c0) + 70
>>>>  >>  _startup(0xfe000000,0x10000000,0xfa000000,0xf00e2bfc,0x10,0xdbc00) + 1414
>>>>  >>  _main(0xf00e0fb4,0xf0007810,0x293ff49f,0xa805209c,0x200,0xf00d1d18) + 14
>>>>  >>
>>>>  >>  Unfortunately (but not surprisingly) kadb doesn't allow debugging
>>>>  >>  cache-flush code, so I can't check what is in
>>>>  >>  [%g5] (aka sfar) on the real machine when this happens.
>>>>  >
>>>>  > Linux code for Swift/TurboSPARC VAC flush should be similar.
>>
>> Do you have an idea why would anyone try reading a value referenced in sfar?
>> Especially during flushing? I can't imagine a case where it wouldn't
>> produce a fault.
>
> No idea, the fault should be inevitable. An explanation how VAC
> (Virtually Addressed Cache?) works could help.

Is it available somewhere? An explanation how PAC works is interesting
too, cause when emulating SS-20, Solaris boots hangs where it normally
says that PAC is initialized.

>>>>  >>  But the bug in phys_page_find would explain this accesses: sfar gets
>>>>  >>  the wrong address, and then the secondary access happens on this wrong
>>>>  >>  address instead of the original one.
>>>>  >
>>>>  > I doubt phys_page_find can be buggy, it is so vital for all architecture.
>>>>
>>>>
>>>> But you've seen the example of buggy behaviour I posted last Friday, right?
>>>>  If it's not phys_page_find, it's either cpu_physical_memory_rw (which
>>>>  is also pretty generic), or
>>>>  the way SS-20 registers devices. Can it be that all the pages must be
>>>>  registered in the proper order?
>>>
>>> How about unassigned access handler, could it be suspected?
>>
>> Doesn't look like it: it gets a physical address as a parameter. How
>> would it know the address is wrong?
>
> It wouldn't, but IIRC Paul claimed earlier that the unassigned memory
> handling in QEMU could have problems.

But I thought Paul also fixed the problems? There was a patch from him.

>>>>  I think it's a pretty rare use case where you have a memory fault (not
>>>>  a translation fault) on an unknown address. You may have such fault
>>>>  during device probing, but in such case you know what address you are
>>>>  probing, so you don't care about the sync fault address register.
>>>>
>>>>  Besides, do all architectures have sync fault address register?
>>>
>>> No, I think system level checks like that and IOMMU-like controls on
>>> most architectures are very poor compared to Sparc32. Server and
>>> mainframe systems may be a bit better.
>>
>> And do we have any mainframe emulated good enough to have a user base
>> and hence bug reports?
>
> The only IOMMU implemented is Sparc32 one so far. I don't know about
> S390x architecture, that should definitely be mainframe class. AMD
> IOMMU may be in QEMU one day.
>
> About bugs, IIRC NetBSD 3.x crash could be related to IOMMU.

What does indicate it? It happens where the disk sizes are normally
reported, so it could be a scsi/dma/irq/fpu issue as well.

>>>>  >>  fwiw the routine is called only once on the real hardware. It sort of
>>>>  >>  speaks for your hypothesis about the memory probing. Although it may
>>>>  >>  not necessarily probe for memory...
>>>>  >>


-- 
Regards,
Artyom Tarasenko

solaris/sparc under qemu blog: http://tyom.blogspot.com/