Allow vm_fault_quick_hold_pages() to specify that nofault mode should be honored.
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Authored by kib on Mar 24 2018, 2:02 PM.

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markj
alc

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rS331557: Allow to specify for vm_fault_quick_hold_pages() that nofault mode

Summary

This is a bit from D14633 needed to implement copyout(9).

We must not sleep or acquire any MI VM locks if TDP_NOFAULTING is specified. On the other hand, there were some callers in the tree which set TDP_NOFAULTING for larger scope than needed, I fixed the code which I wrote, but I suspect that linuxkpi and out of tree drm drivers might abuse this still.

So I only enable the mode for vm_fault_quick_hold_pages() where vm_fault_hold() is not called when specifically asked by user. I decided to use vm_prot_t flag to not change KPI. Since number of flags in vm_prot_t is limited, I reused the same flag which was already consumed for vm_map_lookup().

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rS FreeBSD src repository - subversion

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Event Timeline

kib created this revision.Mar 24 2018, 2:02 PM

Herald added a subscriber: imp. · View Herald TranscriptMar 24 2018, 2:02 PM

Harbormaster completed remote builds in B15771: Diff 40688.Mar 24 2018, 2:02 PM

markj accepted this revision.Mar 24 2018, 3:45 PM

markj added inline comments.

sys/vm/vm.h
83 ↗	(On Diff #40688)	This is pedantic but 0x10 would look more correct. vm_prot_t is only 8 bits wide.
sys/vm/vm_fault.c
1526 ↗	(On Diff #40688)	I'd add a comment explaining the motivation for QUICK_NOFAULT here.

This revision is now accepted and ready to land.Mar 24 2018, 3:45 PM

Mark' notes.

This revision now requires review to proceed.Mar 24 2018, 4:01 PM

markj accepted this revision.Mar 24 2018, 6:18 PM

markj added inline comments.

sys/vm/vm_fault.c
1529 ↗	(On Diff #40694)	There should be a comma after i.e. I would remove the comma after "sleep."
1530 ↗	(On Diff #40694)	"which means we must not call vm_fault_hold()"?
1532 ↗	(On Diff #40694)	"too wide a code area"