From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Wed, 29 May 2013 18:33:28 +0100 Subject: [PATCH V4] ARM: handle user space mapped pages in flush_kernel_dcache_page In-Reply-To: References: <1368336956-6693-1-git-send-email-gmbnomis@gmail.com> <20130523104303.GC16722@arm.com> <20130528095528.GA14329@arm.com> <20130529103728.GG17767@MacBook-Pro.local> Message-ID: <20130529173328.GS17767@MacBook-Pro.local> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, May 29, 2013 at 05:32:50PM +0100, Nicolas Pitre wrote: > On Wed, 29 May 2013, Nicolas Pitre wrote: > > > On Wed, 29 May 2013, Catalin Marinas wrote: > > > > > On Tue, May 28, 2013 at 06:52:27PM +0100, Nicolas Pitre wrote: > > > > On Tue, 28 May 2013, Catalin Marinas wrote: > > > > > > > > > On Sat, May 25, 2013 at 04:53:19AM +0100, Nicolas Pitre wrote: > > > > > > On Thu, 23 May 2013, Catalin Marinas wrote: > > > > > > > > > > > > > An issue is that for kunmap_atomic() && VIVT we flush the same page > > > > > > > twice. I don't think we should remove the cache flushing in > > > > > > > __kunmap_atomic() for VIVT since not all kunmap_atomic() calls require > > > > > > > flush_kernel_dcache_page() (unless we just assume that highmem && vivt > > > > > > > don't work together). > > > > > > > > > > > > VIVT and highmem do work together. Highmem for ARM was in fact > > > > > > developed on such a platform. > > > > > > > > > > Thanks for confirming. Do you remember why kunmap() doesn't (need to) > > > > > flush the cache alias (for VIVT)? Or if it does, where? > > > > > > > > kunmap() calls kunmap_high() which actually does not unmap anything but > > > > only decrement a use count. The page is kept around in case it is > > > > kmap()'d again, in which case the kmap() will be almost free and the > > > > page still warm. > > > > > > > > It is only when the kmap() for a new page runs out of free pkmap > > > > entries that the unused but still mapped pages are unmapped. This > > > > unmapping is done in flush_all_zero_pkmaps() where all the unused pages > > > > are all unmapped at once. The cache for all those pages is flushed with > > > > flush_cache_kmaps() which on ARM maps to flush_cache_all() when the > > > > cache is VIVT. > > > > > > Thanks for clarification Nico. So if kmap_high_get() returns NULL, there > > > are no high aliases left in the cache. > > > > Exact. > > Just to be clear, this is true for VIVT only. > Unmapped highmem pages can still be cached with VIPT. Indeed. -- Catalin