Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [PATCH v2] x86/paravirt: Drop {read,write}_cr8() hooks | Date | Mon, 15 Jul 2019 18:17:59 +0000 |
| |
> On Jul 15, 2019, at 8:16 AM, Andrew Cooper <andrew.cooper3@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.
| |