Messages in this thread | | | Subject | Re: Access to non-RAM pages | From | Benjamin Herrenschmidt <> | Date | Mon, 03 Sep 2018 10:55:42 +1000 |
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On Mon, 2018-09-03 at 10:48 +1000, Benjamin Herrenschmidt wrote: > On Sat, 2018-09-01 at 11:06 -0700, Linus Torvalds wrote: > > [ Adding a few new people the the cc. > > > > The issue is the worry about software-speculative accesses (ie > > things like CONFIG_DCACHE_WORD_ACCESS - not talking about the hw > > speculation now) accessing past RAM into possibly contiguous IO ] > > > > On Sat, Sep 1, 2018 at 10:27 AM Linus Torvalds > > <torvalds@linux-foundation.org> wrote: > > > > > > If you have a machine with RAM that touches IO, you need to disable > > > the last page, exactly the same way we disable and marked reserved the > > > first page at zero. > > So I missed the departure of that train ... stupid question, with > CONFIG_DCACHE_WORD_ACCESS, if that can be unaligned (I assume it can), > what prevents it from crossing into a non-mapped page (not even IO) and > causing an oops ? Looking at a random user in fs/dcache.c its not a > uaccess-style read with recovery.... Or am I missing somethign obvious > here ?
Also, if we cross page boundaries with those guys then we have a bigger problem no ? we could fall off a vmalloc page into the nether or into an ioremap mapping no ?
Cheers, Ben.
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