2017-09-29 9:04 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: > The issue is reported in xen community. > > Anthony PERARD pointed out: > > https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxx/msg117283.html# > > | When developing PVH for OVMF, I've used the lapic timer. It turns out that the > | way it is used by OVMF did not work with Xen [1]. I tried to find out how > | real-hw behave, and write a XTF tests [2]. And this patch series tries to fix > | the behavior of the vlapic timer. > | > | > | The OVMF driver for the APIC timer initialize the timer like this: > | write to TMICT (initial counter) > | write to TMDCR (divide configuration) > | enable the timer (this may change timer mode from one-shot to periodic) > | It turns out that TMICT is set to 0 on the last step, but OVMF expect the timer > | to run. > | > | Here is some description of the APIC timer, base on observation as well as read > | of the Intel SDM. The description is also patch of patch description > | (reworded). > | > | Maybe a way of thinking how the APIC timer is evaluated, is to think of how > | hardward will do it. There is a counter TMCCT which always keeps counting down. > | > | Setting TMICT also set TMCCT, nothing else matter. > | Setting LVTT does not change anything right away. > | Setting TMDCR does not change much. > | > | Now TMCCT keeps counting down, by a value related to TMDCR. > | Once, TMCCT reach 0, it is only at this time that LVTT is taken into account. > | Is there an interrupt to deliver? Should the timer restart counting from the > | value in TMICT? > | > | In the Intel SDM, there is the word "disarm" of the timer used. I guess the > | easier way to disarm the APIC timer (when in periodic or one-shot) is to set > | TMICT to 0. But if we take TSC-Deadline mode out of the picture, there is > | nothing in the manual that say that the timer is disarm or stopped when > | changing timer mode (there is only two modes left, period and one-shot). > | > | As for the TSC-deadline timer mode, observation shown that changing to it (or > | from it) does reset and disarm both timers, so effectively TMICT and the > | tscdeadline are set to 0. > | > | [1] https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg00959.html > | [2] v1: > | https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg02533.html > | v2: look for "[XTF PATCH V2 0/3] Testing vlapic timer" > > In addition, Patch 3/4 implements the illegal vector error handling according to > SDM 10.5.2~10.5.3. > > v1 -> v2: > * add cover-letter and collect recent lapic patches to one patchset > > Wanpeng Li (4): > KVM: LAPIC: Fix lapic timer mode transition > KVM: LAPIC: Keep timer running when switching between one-shot and periodic mode > KVM: LAPIC: Apply change to TDCR right away to the timer > KVM: LAPIC: Don't silently accept bad vectors I just sent out a new version of patch 1~3 for v3, and patch 4 need more time to verify. Regards, Wanpeng Li > > arch/x86/include/asm/apicdef.h | 1 + > arch/x86/kvm/lapic.c | 90 ++++++++++++++++++++++++++++++++++-------- > 2 files changed, 74 insertions(+), 17 deletions(-) > > -- > 2.7.4 >
