> >>> However, you should at least change the comment in vcpu_enter_guest > >>> to mention "before reading PIR" instead of "before reading PIR.ON". > >> > >> Will do that. I think the "checking PIR.ON" should be PID.ON. I will fix > >> it. > >> > > Hi Paolo, > > I reconsidered the comment in vcpu_enter_guest() and think it may don't > > need to change. The original comment as below: > > * 2) For APICv, we should set ->mode before checking PIR.ON. This > > * pairs with the memory barrier implicit in pi_test_and_set_on > > * (see vmx_deliver_posted_interrupt). > > > > I think "before checking PIR.ON" is mean "before checking PID.PIR and > > PID.ON". > > I can say it only means PID.ON because I wrote the comment. :) > > The idea is that checking ON is enough: KVM assumes that PID.PIR is only set > if PID.ON is set, because it follows the definition of ON in table > 29-1 of the SDM: "If this bit is set, there is a notification outstanding for > one or more posted interrupts in bits 255:0". > > VT-D breaks this assumption whenever SN=1 ("hardware does not generate > notification event nor modify the ON field"), resulting in > nonzero PID.PIR but PID.ON=0. I'm sure there was a reason for that, but it > does result in inconsistency between the PID definitions in the > SDM and the VT-D specification. The right fix is definitely to reconcile > this difference and test the bitmap after SN is cleared (with > smp_mb__after_atomic after clearing SN), and set ON=1 if the bitmap is not > clear. > Hi Paolo Thanks for your elaboration, very clear to me. I will fix it in next version.
Thanks, Luwei Kang