Re: [Qemu-devel] [PATCH] e1000: work around win 8.0 boot hang

[Wei Huang <wei@redhat.com>]

On 02/24/2015 05:46 AM, Stefan Hajnoczi wrote:
> On Tue, Feb 24, 2015 at 11:35 AM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> On Thu, Feb 19, 2015 at 08:24:19PM +0100, Radim Krčmář wrote:
>>> Window 8.0 driver has a particular behavior for a small time frame after
>>> it enables rx interrupts:  the interrupt handler never clears
>>> E1000_ICR_RXT0.  The handler does this something like this:
>>>   set_imc(-1)               (1) disable all interrupts
>>>   val = read_icr()          (2) clear ICR
>>>   handled = magic(val)      (3) do nothing to E1000_ICR_RXT0
>>>   set_ics(val & ~handled)   (4) set unhandled interrupts back to ICR
>>>   set_ims(157)              (5) enable some interrupts
>>>
>>> so if we started with RXT0, then every time the handler re-enables e1000
>>> interrupts, it receives one.  This likely wouldn't matter in real
>>> hardware, because it is slow enough to make some progress between
>>> interrupts, but KVM instantly interrupts it, and boot hangs.
>>> (If we have multiple VCPUs, the interrupt gets load-balanced and
>>>  everything is fine.)
>>>
>>> I haven't found any problem in earlier phase of initialization and
>>> windows writes 0 to RADV and RDTR, so some workaround looks like the
>>> only way if we want to support win8.0 on uniprocessors.  (I vote NO.)
>>>
>>> This workaround uses the fact that a constant is cleared from ICR and
>>> later set back to it.  After detecting this situation, we reuse the
>>> mitigation framework to inject an interrupt 10 microseconds later.
>>> (It's not exactly 10 microseconds, to keep the existing logic intact.)
>>>
>>> The detection is done by checking at (1), (2), and (5).  (2) and (5)
>>> require that the only bit in ICR is RXT0.  We could also check at (4),
>>> and on writes to any other register, but it would most likely only add
>>> more useless code, because normal operations shouldn't behave like that
>>> anyway.  (An OS that deliberately keeps bits in ICR to notify itself
>>> that there are more packets, or for more creative reasons, is nothing we
>>> should care about.)
>>>
>>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>>> ---
>>>  The patch is still untested -- it only approximates the behavior of RHEL
>>>  patches that worked, I'll try to get a reproducer ...
>>>
>>>  hw/net/e1000.c | 29 ++++++++++++++++++++++-------
>>>  1 file changed, 22 insertions(+), 7 deletions(-)
>>
>> Hi Alex,
>> I've CCed you in case you have any advice regarding QEMU's e1000
>> emulation.  It seems Windows 8 gets itself into a kind of interrupt
>> storm and a workaround in QEMU will be necessary.
>>
>> Any thoughts?
> 
> Okay, I guess Alex has changed jobs since the email has bounced.  Too
> bad, it was worth a shot.
> 
> Regarding the workaround, I'm okay with it.  It's a hack for sure but
> what other option do we have?
> 
I wasn't able to reproduce this problem with upstream QEMU. According to
Radim, this bug requires a very subtle timing during guest installation.
So probably my testing didn't hit the right timing. Additionally our QE
confirmed that this patch fixed a Win8 installation issue that were seen
on in-house QEMU (e.g. qemu-kvm-rhev). With that, I am OK with this
patch. The only thing left is to fix the compilation in this patch (as
Radim pointed out). Anyway,

Reviewed-by: Wei Huang <wei@redhat.com>

Thanks,
-Wei

> Stefan
>