KAMEZAWA Hiroyuki wrote:
On Wed, 04 Jul 2007 16:31:06 +1000
Nick Piggin <[EMAIL PROTECTED]> wrote:
The only thing I noticed when I looked at the code is that some places
may not have flushed icache when they should have? Did you get them all?
I think that I added flush_icache_page() to the place where any
flush_(i)cache_xxx
is not called and lazy_mmu_prot_update was used instead of them.
But I want good review, of course.
Minor nitpick: you have one place where you test VM_EXEC before flushing,
but the flush routine itself contains the same test I think?
Ah, yes...in do_anonymous_page(). my mistake.
Regarding the ia64 code -- I'm not an expert so I can't say whether it
is the right thing to do or not. However I still can't work out what it's
rationale for the PG_arch_1 bit is, exactly. Does it assume that
flush_dcache_page sites would only ever be encountered by pages that are
not faulted in? A faulted in page kind of is "special" because it is
guaranteed uptodate, but is the ia64 arch code relying on that? Should it?
(I'm sorry if I misses point.)
ia64's D-cache is coherent but I-cache and D-cache is not coherent and any
invalidation against d-cache will invalidate I-cache.
In my understanding :
PG_arch_1 is used for showing "there is no inconsistent data on any level of
cache". PG_uptodate is used for showing "this page includes the newest data
and contents are valid."
...maybe not used for the same purpose.
I think that's right, but why is set_pte-time the critical point for the
flush? It is actually possible to write into an executable page via the
dcache *after* it has ptes pointing to it.
From what I can work out, it is something like "at this point the page
should be uptodate, so at least the icache won't contain *inconsistent*
data, just old data which userspace should take care of flushing if it
modifies". Is that always true? Could the page get modified by means
other than a direct write(2)? And even in the case of a write(2) writer,
how do they know if another process is mapping that particular page for
exec at that time? Should they always flush? Flushing would require they
have a virtual address on the page to begin with anyway, doesn't it? So
they'd have to mmap it... phew.
I guess it is mostly safe because it is probably very uncommon to do
such a thing, and chances are no non-write(2) write activity happens to
a page after it is brought uptodate. But I don't know if that has been
audited. I would really like to see the kernel always manage all aspects
of its pagecache though. I realise performance considerations may make
this not always possible... but it might be possible to do efficiently
using mapcount these days?
Anyway, ignore my tangent if you like :) Your patch doesn't make any of
this worse, so I'm getting off topic.
So I think your patch is nice, but would need ia64 people to actually ack
it.
BTW, a page filled by DMA should have PG_arch_1 :(
The consequences of not are superfluous flushes?
--
SUSE Labs, Novell Inc.
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