Hi Nick,
-----Original Message-----
From: Nick Piggin [mailto:nickpiggin@xxxxxxxxxxxx] Sent: Friday, April 27, 2007 11:03 PM
To: Hugh Dickins
Cc: rohitseth@xxxxxxxxxx; Mike Stroyan; Andrew Morton; Luck, Tony;
linux-ia64@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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? [*]).
It is invalidating any entries (containing same physical address) in both I
and D caches. Any dirty lines in D cache are written back to memory before
getting invalidated (ofcourse).
There are supposedly no icache lines at that point[**]:
For this bug to trigger there has to be a (stale) entry in icache containing
the old contents of a page that just got updated by kernel as explicit
copying of data (DMAs are coherent on ia64, meaning if a device were to
write to memory then architecture guarnatees that both I and D caches are
invalidated).