On 16/07/2019 01:05, Andy Lutomirski wrote: > On Mon, Jul 15, 2019 at 4:30 PM Andrew Cooper <andrew.coop...@citrix.com> > wrote: >> On 15/07/2019 19:17, Nadav Amit wrote: >>>> On Jul 15, 2019, at 8:16 AM, Andrew Cooper <andrew.coop...@citrix.com> >>>> wrote: >>>> >>>> There is a lot of infrastructure for functionality which is used >>>> exclusively in __{save,restore}_processor_state() on the suspend/resume >>>> path. >>>> >>>> cr8 is an alias of APIC_TASKPRI, and APIC_TASKPRI is saved/restored by >>>> lapic_{suspend,resume}(). Saving and restoring cr8 independently of the >>>> rest of the Local APIC state isn't a clever thing to be doing. >>>> >>>> Delete the suspend/resume cr8 handling, which shrinks the size of struct >>>> saved_context, and allows for the removal of both PVOPS. >>> I think removing the interface for CR8 writes is also good to avoid >>> potential correctness issues, as the SDM says (10.8.6.1 "Interaction of Task >>> Priorities between CR8 and APIC”): >>> >>> "Operating software should implement either direct APIC TPR updates or CR8 >>> style TPR updates but not mix them. Software can use a serializing >>> instruction (for example, CPUID) to serialize updates between MOV CR8 and >>> stores to the APIC.” >>> >>> And native_write_cr8() did not even issue a serializing instruction. >>> >> Given its location, the one write_cr8() is bounded by two serialising >> operations, so is safe in practice. >> >> However, I agree with the statement in the manual. I could submit a v3 >> with an updated commit message, or let it be fixed on commit. Whichever >> is easiest. >> > I don't see anything wrong with the message. If we actually used CR8 > for interrupt priorities, we wouldn't want it to serialize. The bug > is that the code that did the write_cr8() should have had a comment as > to how it serialized against lapic_restore(). But that doesn't seem > worth mentioning in the message, since, as noted, the real problem was > that it nonsensically restored just TPR without restoring everything > else.
Fair enough, in which case I'm happy with v2 as it is. ~Andrew _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization