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Differential D59749

vmm: Normalize a zero PIT count before starting channel 0
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Authored by hayzam_gmail.com on Thu, Sep 17, 12:08 AM.
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bcran
imp
rgrimes

Details

Reviewers
markj
Group Reviewers
bhyve
Summary

pit_timer_start_cntr0() does not schedule a callout when the initial
count is zero. The counter write handler normalizes a programmed zero
count only after calling it, leaving an initially unarmed channel 0
without a scheduled timer event.

Move the existing normalization before the timer-start call. Retain the
historical 0xffff representation of a zero count.

Sponsored by: The FreeBSD Foundation

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Repository
rG FreeBSD src repository
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Unit
Tests Skipped
Build Status
Buildable 77006
Build 73889: arc lint + arc unit

Event Timeline

hayzam_gmail.com created this revision.Thu, Sep 17, 12:08 AM
Herald added a reviewer: bhyve. · View Herald TranscriptThu, Sep 17, 12:08 AM
Herald added subscribers: bcran, rgrimes, imp. · View Herald Transcript
hayzam_gmail.com requested review of this revision.Thu, Sep 17, 12:08 AM
Harbormaster completed remote builds in B77006: Diff 186927.Thu, Sep 17, 12:08 AM
markj accepted this revision as: markj.Thu, Sep 17, 1:48 PM

How did you notice the problem?

This revision is now accepted and ready to land.Thu, Sep 17, 1:48 PM
hayzam_gmail.com added a comment.EditedThu, Sep 17, 1:57 PM
In D59749#1371481, @markj wrote:

How did you notice the problem?

The symptom was a legacy guest hanging at the BIOS screen with its tick frozen while I was bringing up CSMWrap (https://github.com/CSMWrap/CSMWrap) on bhyve. I traced that back to SeaBIOS programming the PIT with a zero count for the normal ~18 Hz tick, which led me to this code.

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sys/
amd64/
vmm/
io/
4 lines

Diff 186927

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sys/amd64/vmm/io/vatpit.c

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