Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path

From: Nick Piggin
Date: Sat Apr 28 2007 - 02:03:59 EST

Hugh Dickins wrote:
On Sat, 28 Apr 2007, Nick Piggin wrote:

OIC, you need a virtual address to evict the icache, so you can't
flush at flush_dcache time? Or does ia64 have an instruction to
flush the whole icache? (it would be worth testing, to see how much
performance suffers).

I'm puzzled by that remark: the ia64 flush_icache_range always has
a virtual address, it uses the kernel virtual address; it takes no
interest in whether there's a user virtual address.

I _think_ what it is doing is actually flushing dcache lines dirtied
via the kernel virtual address (yes, I think flush_icache in
lazy_mmu_prot_update is actually just flushing the dcache, but I could
be wrong? [*]). There are supposedly no icache lines at that point[**]:
the bug fix at the start of this thread is due to icache lines
becoming present before the flush.

[*] and if I'm right, that means that icache fills don't see dirty
dcache, but rather always load from memory? I hope someone can
answer these questions?

[**] except due to _existing_ executable mappings, of course, but they
seem to have been comprehensively disregarded...

SUSE Labs, Novell Inc.
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