On Mon, Sep 8, 2014 at 2:55 PM, Rabin Vincent <ra...@rab.in> wrote: > On Mon, Sep 08, 2014 at 12:16:34PM -0700, Kees Cook wrote: >> On Thu, Sep 04, 2014 at 06:27:48PM +0100, Will Deacon wrote: >> > On Thu, Sep 04, 2014 at 06:23:42PM +0100, Kees Cook wrote: >> > > Ah! If this is the case, perhaps we can get away with >> > > local_flush_tlb_kernel_range() then? >> > >> > That's a bit tricky, since you need to ensure that preemption is disabled >> > until the mapping is put back like it was. >> >> Okay, under both real hardware with the errata, and under QEMU, things seem >> to work with this change to the series. What do you think? > > Preemption is already disabled until the mapping is put back in this > patch.c code because interrupts are disabled from before the time > set_fixmap() is called until after clear_fixmap() is called.
Should I drop the preempt_disable/enable(), and just add a comment to set_fixmap()? > I'd guess that Will meant other (future) callers of set_fixmap() would > have to ensure similar behaviour with set_fixmap() / clear_fixmap(). > > Unless I'm missing something set/clear_fixmap() seem to be quite arch > specific and only really used on x86, so we could ensure that future > users on ARM perform the correct tlb flush: the first user on ARM with > a non-atomic context (or you) could implement a set_fixmap() which does > the global flush and have this patch.c (and any other atomic context > callers) call __set_fixmap() directly. > > The change to local_flush_tlb_kernel_range() in __set_fixmap() would of > course be needed in that case, and IIRC that was what my original patch > had (via set_top_pte()). Ah, so it was, yes! Will, which version of this logic would you prefer? Thanks! -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
