linux-kernel - Re: Fw: [PATCH] ia64: race flushing icache in do_no

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Date:	Sat, 28 Apr 2007 16:03:28 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Hugh Dickins <hugh@...itas.com>
CC:	rohitseth@...gle.com, Mike Stroyan <mike.stroyan@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Luck, Tony" <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path

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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