Hello all;
I've been working on improving the AHCI device emulation for QEMU but
have recently run into an issue where Windows 8 guests -- upon trying to
resume from hibernation -- manage to trigger an infinite IRQ injection
loop where it seems that the IRQ never quite properly gets cleared.
I am still working on troubleshooting it further, but I wanted to see if
anyone had advice or experience with this type of issue.
In a nutshell:
- Windows 8 boots up inside of QEMU/KVM
- Windows 8 is suspended to disk either via "shut down" or explicit
hibernate. QEMU exits.
- Windows 8 is resumed
- Windows 8 resets the AHCI device and begins re-initializing it
- Once the active AHCI port is reset, it issues an interrupt to indicate
it has a pending message (set of register values) ready for the host to
synchronize state with the HBA. This interrupt appears to be legacy PCI
and not MSI.
- This triggers an infinite injection loop.
Here are some characteristic traces from perf record, grabbing
kvm-related entries with user space traces.
Here's where the interrupt first appears to become stuck, showing when
it is set: http://pastebin.com/KPevxCw2
It looks like pin #16, vec=177. All activity in the guest and QEMU now
apparently ceases, and then the perf script shows many, many loops which
look like the following: http://pastebin.com/qYh9035y
which repeats over-and-over. It does not appear that QEMU is re-setting
the IRQ, and there are no further calls from the guest into ICH9 or AHCI
related code to set/unset any device registers.
In talking with Stefan, we think that the irr bit is possibly not
getting cleared (or getting set again?) after the EOI (see the first
paste) -- does anyone have experience with debugging this type of issue,
or have some hints about what may be happening?
Thanks in advance for any advice.
--John S.
(As a post-script: the kernel I am using is the version provided by
David Airlie for MST [Multi-Stream Transport] support in Linux, which is
still experimental. Sorry for the non-stock kernel!
http://airlied.livejournal.com/79657.html)
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