On Fri, Mar 2, 2012 at 5:02 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>
> Note that does mean we need a guard page after each and every
> discontiguous RAM range, not just the last one. Raising that issue
> since we have had serious bugs in that area in the past.
Are you sure? I didn't think we even *mapped* things at that granularity.
We only really need a guard page at the end of an actual end-of-ram
where we no longer have page tables and/or could hit device space.
Which in practice never actually is an issue on PC's - we already
guard against BIOS usage just under the 0xA0000 address, and in
practice there are always ACPI tables at the end of RAM (and on x86-32
we can't use highmem for filenames anyway, so that takes away *those*
cases).
Which is why I think that for testing purposes we don't even need to
care - it's basically a "can't happen" (not to mention that nobody
actually uses PATH_MAX pathames).
For robustness and actual deployment, I do think that yes, we do want
to make it an explicit rule.
Linus
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