Re: fixmap TLB flushing clarification

[Manfred Spraul]

> I'm curious about the last statement, is this to mean that a TLB entry will
> be reserved at set_fixmap() time in which the translation will happen, and
> that particular entry will be locked down for the duration of the mapping?
>  
No. fixmap mappings are global - identical for all processes and all 
cpus. Therefore it's not necessary to flush them during a task switch. 
But that's just an optimization, not a mandatory feature:
On x86 it's possible to mark page table entries as global. Global 
entries are not flushed by the normal tlb flush command, this gives a 
slighly better performance. If your architecture doesn't support that, 
then you can just flush everything during a task switch. I think the 
support for global entries was added for the Pentium cpus - 80486 cpus 
flush the whole tlb cache during a task switch.

--
   Manfred



-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/