Gleb Natapov wrote: > On Sat, Feb 13, 2010 at 07:41:35PM +0100, Jan Kiszka wrote: >> Gleb Natapov wrote: >>> On Sat, Feb 13, 2010 at 06:49:44PM +0100, Jan Kiszka wrote: >>>> Gleb Natapov wrote: >>>>> On Sat, Feb 13, 2010 at 10:51:40AM +0100, Jan Kiszka wrote: >>>>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>>>> >>>>>> VMX requires a properly set instruction length VM entry field when >>>>>> trying to inject soft exception and interrupts. We have to preserve this >>>>>> state across VM save/restore to avoid breaking the re-injection of such >>>>>> events on Intel. So add it to the new VCPU event state. >>>>>> >>>>> We shouldn't re-inject soft exceptions/interrupts after migration, but >>>>> re-execute instruction instead. Instruction length field doesn't exist >>>>> on SVM and migration shouldn't expose implementation details. >>>>> >>>> Hmm, then I guess this totally untested patch should fly: >>>> >>> I don't understand what problem are you trying to solve by your patch. >>> During normal operation event_exit_inst_len will be set to correct >>> value. After migration rip will point to int instruction an no even will >>> be pending at all. Here is the patch: >> The patch will cause an endless loop if BP interception is enabled. >> > How? This code path is not executed normally. Oh, I read it the other way around, but it is supposed to mask soft exceptions/irqs (clearing *.injected is missing then). > >> What is the purpose of keeping event_exit_inst_len around? Either we >> need it also across user space exists, then we have to save/restore or >> reconstruct it, or we don't need it, then simply drop it. >> > Why we need to save/restore is if we need it across user space exits? > We need to save/restore it only if we nedd it across migration. > > When exception happens during soft interrupt/exception delivery soft i/e > should be retried somehow. There are two ways to do that. First one is just > reenter guest with the same rip. Instruction will be reexecuted and > event redelivered. Another is to reinject event via event reinjection > mechanism and for that we need to tell CPU how to calculate rip of a next > instruction and this is done by providing event_exit_inst_len. The But I still fail to see the case where event_exit_inst_len is set to anything but 1 or 2 and where it is related to anything else than exits at INT3, INT X, or INTO. > problem is that SVM supports only the first way. Intel advised us to use > reinjection mechanism, so that what we use on VMX, but since migration > can happen from Intel to AMD and vice versa we chose to reexecute > instruction after migration on those rare occasions that migration > happens exactly after intercepted soft i/e. Jan
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