Re: [patch -mm series] ia64 specific /dev/mem handlers

From: Jes Sorensen
Date: Thu Mar 10 2005 - 08:51:02 EST

>>>>> "Andrew" == Andrew Morton <akpm@xxxxxxxx> writes:

Andrew> Jes Sorensen <jes@xxxxxxxxxxxxxxxxxx> wrote:
>> Convert /dev/mem read/write calls to use arch_translate_mem_ptr if
>> available. Needed on ia64 for pages converted fo uncached mappings
>> to avoid it being accessed in cached mode after the conversion
>> which can lead to memory corruption. Introduces PG_uncached page
>> flag for marking pages uncached.

Andrew> For some reason this patch still gives me the creeps. Maybe
Andrew> it's because we lose a page flag for something so obscure.

Andrew> Nothing ever clears PG_uncached. We'll end up with every page
Andrew> in the machine marked as being uncached.

Actually there's restrictions to how many pages are getting converted
as converting pages over from cached to uncached isn't trivial on ia64.

Andrew> But then, nothing ever sets PG_uncached, either. Is there
Andrew> some patch which you're hiding from me?

Actually I posted that earlier, but it must have gotten lost in the
noise. It's part of the genalloc/mspec patchset. I'll send it to you

Andrew> If a page is marked uncached then it'll remain marked as
Andrew> uncached even after it's unmapped. Or will it? Would like to
Andrew> see the other patch, please.

Coming your way in a jiffy.

Andrew> We should add PG_uncached checks to the page allocator. Is
Andrew> this OK?

I don't see any problems with that. The way it's meant to be used is
that once pages are converted over, they don't go back into the

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