Thanks for catching.
> why this bug never become prominent is a mystery - it can probably be
> explained with the (still) relative obscurity of the x86_64 architecture.
global_flush_tlb() is not very common in the big scheme of things. In a normal
system it only happens single threaded during X server startup and when
the system starts.
So while it's nasty it's unlikely to really hit people in practice.
BTW while looking I noticed this code in the vermilion driver is also
surely not correct:
/*
* Change caching policy of the linear kernel map to avoid
* mapping type conflicts with user-space mappings.
* The first global_flush_tlb() is really only there to do a global
* wbinvd().
*/
global_flush_tlb();
That is not what gft is guaranteed to do.
It would be probably best to just do away with g_f_t() and fold it directly into
c_p_a(). I've seen little evidence the delayed flush optimization ever made
much difference and it seems to be misused and a source of bugs. And near all
legitimate users seem to always call it directly after c_p_a() anyways.
Besides it is grossly misnamed -- it does much more than flushing TLBs.
-Andi
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