On Wed, 2009-10-14 at 18:10 +0100, Catalin Marinas wrote: > On Tue, 2009-10-13 at 11:07 +0900, Paul Mundt wrote: > > On Mon, Oct 12, 2009 at 06:03:12PM +0100, Russell King wrote: > > > I don't see that there should have been any bearing on whether a page > > > has a mapping or not when we get to update_mmu_cache. The issue here > > > is that > if PG_arch_1 is set on a page, then we didn't flush it at > > > the time when we believed it was appropriate to do so. < > > > > > > Tell me I'm wrong (having only just sent it to Linus...) > > > > Having looked at the ARM fix, in the !mapping case do you not need the > > I-cache flush on vma->vm_flags & VM_EXEC? Or is the presumption that > > flush_icache_page()-type action doesn't need to be undertaken by > > flush_dcache_page()/update_mmu_cache() when there is no page_mapping()? > > If I understand Nitin's scenario correctly, I think it should also > invalidate the I-cache. > > For executable anonymous pages containing, it's the user app writing the > code (JIT etc.) and it calls an ARM-specific syscall for I and D cache > maintenance. If such page is read back from swap, following Nitin's > scenario, the I-cache would need to be invalidated as well otherwise it > can have stale entries. We can have a scenario where I-cache invalidation would not help on ARM. Some apps may temporarily change protection from RX to RW to write some data (not instructions) to a page containing code. If Nitin's scenario happens when the page is RW, the VM_EXEC wouldn't be set, hence no I-cache invalidation. The app would later do mprotect(RX) but on some ARM processors flush_cache_range() is a no-op and therefore no cache flushing. What other architectures with Harvard caches do for mprotect(RX)? Is this assumed to invalidate the I-cache? (we have another I-D cache coherency problem on ARM with COW text pages following a RX -> RW -> write data -> RX scenario and there are a few solutions for this, though none of them optimal with the current cache flushing API, especially with the read-implies-exec ELF personality) -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
