On Tue, Oct 17, 2017 at 10:34:15AM +0100, Marc Zyngier wrote: > On 16/10/17 21:08, Christoffer Dall wrote: > > On Mon, Oct 09, 2017 at 04:20:28PM +0100, Marc Zyngier wrote: > >> The only case where we actually need to perform a dache maintenance > >> is when we map the page for the first time, and subsequent permission > >> faults do not require cache maintenance. Let's make it conditional > >> on not being a permission fault (and thus a translation fault). > > > > Why do we actually need to do any dcache maintenance when faulting in a > > page? > > > > Is this for the case when the stage 1 MMU is disabled, or to support > > guest mappings using uncached attributes? > > These are indeed the two cases that require cleaning the dcache to PoC. > > > Can we do better, for example > > by only flushing the cache if the guest MMU is disabled? > > The guest MMU being disabled is easy. But the uncached mapping is much > trickier, and would involve parsing the guest page tables. Not something > I'm really eager to implement. > Hmm, if the guest actually maps memory uncached, wouldn't it have to invalidate caches itself, or is this the annoying thing where disabling the MMU on hardware that doesn't have stage 2 would in fact always completely bypass the cache, and therefore we have to do this work? Sorry, I have forgotten all the details here, but wanted to make sure we're not being overly careful. Thanks, -Christoffer
