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" v5 -> v6: * rebase against latest kvm/queue * extract the function limit_periodic_timer_frequency() * rate limit when switching from one-shot to periodic * introduce a new function for updating the expiration when TDCR is changed, and apply the rate limit v4 -> v5: * reflect the runtime divide/rate update for the remaining timer v3 -> v4: * don't need to start_apic_timer() when write LVTT v2 -> v3: * move the write 0 to APIC_TMICT logic to apic_update_lvtt() * skip hrtimer_cancel() in apic_update_lvtt() when either from one-shot mode to periodic or vice versa. v1 -> v2: * add cover-letter and collect recent lapic patches to one patchset Wanpeng Li (3): KVM: LAPIC: Introduce limit_periodic_timer_frequency KVM: LAPIC: Keep timer running when switching between one-shot and periodic mode KVM: LAPIC: Apply change to TDCR right away to the timer arch/x86/kvm/lapic.c | 88 +++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 67 insertions(+), 21 deletions(-) -- 2.7.4
