Re: [PATCH 0/9] Make lazy mmu update mode pre-empt safe

Jeremy Fitzhardinge
2009-02-18T22:52:46Z

[ Clearly some aspect of this mailbomb tool is eluding me. ]

Hi,

This series changes the paravirt-ops lazy update modes in the following
ways:

1. Make paravirt_get_lazy_mode() always return PARAVIRT_LAZY_NONE in
interrupt context. This has the effect of making all mmu and cpu
state updates synchronous in interrupt routines, without the need
to add explicit flushing.

2. De-generalize lazy cpu mode to a specific context-switch operation.
Rather than dealing with fully general enter/leave lazy cpu update
mode, make it specifically about start/end context switch, since that
was the only use anyway. That means the implementations know that
they're in the middle of a context switch.

3. On starting a context switch, if the task is in lazy mmu update mode,
record that fact in thread_info->flags TIF_LAZY_MMU_UPDATE, and
disable lazy updates (flushing anything pending). On ending a context
switch, if the new task has TIF_LAZY_MMU_UPDATE set, then reenter
lazy mmu update mode.

4. Remove all the preempt_disable/enable pairs and assertion that
preemption must be disabled for lazy mmu updates.

This has the net effect of 1) making lazy mmu updates more robust, and
2) not requiring any changes to the current rules of how init_mm can
be updated.

Thanks,
J