On 20.05.14 14:45, Gavin Shan wrote:
On Tue, May 20, 2014 at 02:14:56PM +0200, Alexander Graf wrote:
On 20.05.14 13:56, Gavin Shan wrote:
On Tue, May 20, 2014 at 01:25:11PM +0200, Alexander Graf wrote:
On 20.05.14 10:30, Gavin Shan wrote:
If we detects frozen state on PE that has been passed to guest, we
needn't handle it. Instead, we rely on the guest to detect and recover
it. The patch avoid EEH event on the frozen passed PE so that the guest
can have chance to handle that.
Signed-off-by: Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx>
How does the guest learn about this failure? We'd need to inject an
error into it, no?
When error is existing in HW level, 0xFF's will be turned on reading
PCI config space or memory BARs. Guest retrieves the failure state,
which is captured by HW automatically, via RTAS call
"ibm,read-slot-reset-state2" when seeing 0xFF's on reading PCI config
space or memory BARs. If "ibm,read-slot-reset-state2" reports errors in HW,
the guest kernel starts to recovery.
It can be called as "passive" reporting. There possible has one case that
the error can't be reported for ever: No device driver binding to the VFIO
PCI device and no access to device's config space and memory BARs. However,
it doesn't matter. As we don't use the device, we needn't detect and recover
the error at all.
So if the guest is waiting for an interrupt to happen it will wait
forever? Not really nice.
Nope, the error reporting in guest isn't interrupt-driven. It's always
"polling" :-)
That sucks :).
I think what you want is an irqfd that the in-kernel eeh code
notifies when it sees a failure. When such an fd exists, the kernel
skips its own error handling.
Yeah, it's a good idea and something for me to improve in phase II. We
can discuss for more later.
I think it makes sense to at least walk into that direction
immediately. The reason I brought it up in the context of this patch
is that with an irqfd you wouldn't need the passed flag at all.
I don't see how it can avoid the "passed" flag. Without the flag, any
PCI config and memory BAR access on host side could trigger EEH recovery
for those PCI devices passed to guest. That's unexpected behaviour.
Instead of
if (passed_flag)
return;
you would do
if (trigger_irqfd) {
trigger_irqfd();
return;
}
which would be a much nicer, generic interface.
For host, we have 2 ways to report errors: interrupt driven and polling.
For the guest, we only have "polling" :-)
And the interrupt path is powernv specific? Does sPAPR specify anything
here?
For now, what I have in my head is something
like this:
[ Host ] -> Error detected -> irqfd (or eventfd) -> QEMU
|
-------------(A)---------
|
Send one EEH event to guest kernel
|
Guest kernel starts the recovery
(A): I didn't figure out one convienent way to do the EEH event injection yet.
How does the guest learn about errors in pHyp?
It relies on "polling".
Sigh ;).
So how about we just implement this whole thing properly as irqfd?
Whether QEMU can actually do anything with the interrupt is a different
question - we can leave it be for now. But we could model all the code
with the assumption that it should either handle the error itself or
trigger and irqfd write.
Alex
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