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2010-12-19ARM: get rid of kmap_high_l1_vipt()Nicolas Pitre
Since commit 3e4d3af501 "mm: stack based kmap_atomic()", it is no longer necessary to carry an ad hoc version of kmap_atomic() added in commit 7e5a69e83b "ARM: 6007/1: fix highmem with VIPT cache and DMA" to cope with reentrancy. In fact, it is now actively wrong to rely on fixed kmap type indices (namely KM_L1_CACHE) as kmap_atomic() totally ignores them now and a concurrent instance of it may reuse any slot for any purpose. Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
2010-10-27mm: fix race in kunmap_atomic()Peter Zijlstra
Christoph reported a nice splat which illustrated a race in the new stack based kmap_atomic implementation. The problem is that we pop our stack slot before we're completely done resetting its state -- in particular clearing the PTE (sometimes that's CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear the PTE used for the last slot, that interrupt can reuse the slot in a dirty state, which triggers a BUG in kmap_atomic(). Fix this by introducing kmap_atomic_idx() which reports the current slot index without actually releasing it and use that to find the PTE and delay the _pop() until after we're completely done. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Reported-by: Christoph Hellwig <hch@infradead.org> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-26mm: stack based kmap_atomic()Peter Zijlstra
Keep the current interface but ignore the KM_type and use a stack based approach. The advantage is that we get rid of crappy code like: #define __KM_PTE \ (in_nmi() ? KM_NMI_PTE : \ in_irq() ? KM_IRQ_PTE : \ KM_PTE0) and in general can stop worrying about what context we're in and what kmap slots might be appropriate for that. The downside is that FRV kmap_atomic() gets more expensive. For now we use a CPP trick suggested by Andrew: #define kmap_atomic(page, args...) __kmap_atomic(page) to avoid having to touch all kmap_atomic() users in a single patch. [ not compiled on: - mn10300: the arch doesn't actually build with highmem to begin with ] [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: fix up drivers/gpu/drm/i915/intel_overlay.c] Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Chris Metcalf <cmetcalf@tilera.com> Cc: David Howells <dhowells@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: David Miller <davem@davemloft.net> Cc: Paul Mackerras <paulus@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Dave Airlie <airlied@linux.ie> Cc: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-08-09kmap_atomic: make kunmap_atomic() harder to misuseCesar Eduardo Barros
kunmap_atomic() is currently at level -4 on Rusty's "Hard To Misuse" list[1] ("Follow common convention and you'll get it wrong"), except in some architectures when CONFIG_DEBUG_HIGHMEM is set[2][3]. kunmap() takes a pointer to a struct page; kunmap_atomic(), however, takes takes a pointer to within the page itself. This seems to once in a while trip people up (the convention they are following is the one from kunmap()). Make it much harder to misuse, by moving it to level 9 on Rusty's list[4] ("The compiler/linker won't let you get it wrong"). This is done by refusing to build if the type of its first argument is a pointer to a struct page. The real kunmap_atomic() is renamed to kunmap_atomic_notypecheck() (which is what you would call in case for some strange reason calling it with a pointer to a struct page is not incorrect in your code). The previous version of this patch was compile tested on x86-64. [1] http://ozlabs.org/~rusty/index.cgi/tech/2008-04-01.html [2] In these cases, it is at level 5, "Do it right or it will always break at runtime." [3] At least mips and powerpc look very similar, and sparc also seems to share a common ancestor with both; there seems to be quite some degree of copy-and-paste coding here. The include/asm/highmem.h file for these three archs mention x86 CPUs at its top. [4] http://ozlabs.org/~rusty/index.cgi/tech/2008-03-30.html [5] As an aside, could someone tell me why mn10300 uses unsigned long as the first parameter of kunmap_atomic() instead of void *? Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net> Cc: Russell King <linux@arm.linux.org.uk> (arch/arm) Cc: Ralf Baechle <ralf@linux-mips.org> (arch/mips) Cc: David Howells <dhowells@redhat.com> (arch/frv, arch/mn10300) Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com> (arch/mn10300) Cc: Kyle McMartin <kyle@mcmartin.ca> (arch/parisc) Cc: Helge Deller <deller@gmx.de> (arch/parisc) Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> (arch/parisc) Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> (arch/powerpc) Cc: Paul Mackerras <paulus@samba.org> (arch/powerpc) Cc: "David S. Miller" <davem@davemloft.net> (arch/sparc) Cc: Thomas Gleixner <tglx@linutronix.de> (arch/x86) Cc: Ingo Molnar <mingo@redhat.com> (arch/x86) Cc: "H. Peter Anvin" <hpa@zytor.com> (arch/x86) Cc: Arnd Bergmann <arnd@arndb.de> (include/asm-generic) Cc: Rusty Russell <rusty@rustcorp.com.au> ("Hard To Misuse" list) Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-07-30ARM: 6279/1: highmem: fix SMP preemption bug in kmap_high_l1_viptGary King
smp_processor_id() must not be called from a preemptible context (this is checked by CONFIG_DEBUG_PREEMPT). kmap_high_l1_vipt() was doing so. This lead to a problem where the wrong per_cpu kmap_high_l1_vipt_depth could be incremented, causing a BUG_ON(*depth <= 0); in kunmap_high_l1_vipt(). The solution is to move the call to smp_processor_id() after the call to preempt_disable(). Originally by: Andrew Howe <ahowe@nvidia.com> Signed-off-by: Gary King <gking@nvidia.com> Acked-by: Nicolas Pitre <nico.as.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-06-08ARM: 6165/1: trap overflows on highmem pages from kmap_atomic when debuggingNicolas Pitre
When CONFIG_DEBUG_HIGHMEM is used, the fixmap entry used for a highmem page by kmap_atomic() is always cleared by kunmap_atomic(). This helps find bad usages such as dereferences after the unmap, or overflow into the adjacent fixmap areas. But this debugging aid is completely bypassed when a kmap for the same page already exists as the kmap is reused instead. ON VIVT systems we have no choice but to reuse that kmap due to cache coherency issues, but on non VIVT systems we should always force the fixmap usage when debugging is active. Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-04-14ARM: 6007/1: fix highmem with VIPT cache and DMANicolas Pitre
The VIVT cache of a highmem page is always flushed before the page is unmapped. This cache flush is explicit through flush_cache_kmaps() in flush_all_zero_pkmaps(), or through __cpuc_flush_dcache_area() in kunmap_atomic(). There is also an implicit flush of those highmem pages that were part of a process that just terminated making those pages free as the whole VIVT cache has to be flushed on every task switch. Hence unmapped highmem pages need no cache maintenance in that case. However unmapped pages may still be cached with a VIPT cache because the cache is tagged with physical addresses. There is no need for a whole cache flush during task switching for that reason, and despite the explicit cache flushes in flush_all_zero_pkmaps() and kunmap_atomic(), some highmem pages that were mapped in user space end up still cached even when they become unmapped. So, we do have to perform cache maintenance on those unmapped highmem pages in the context of DMA when using a VIPT cache. Unfortunately, it is not possible to perform that cache maintenance using physical addresses as all the L1 cache maintenance coprocessor functions accept virtual addresses only. Therefore we have no choice but to set up a temporary virtual mapping for that purpose. And of course the explicit cache flushing when unmapping a highmem page on a system with a VIPT cache now can go, which should increase performance. While at it, because the code in __flush_dcache_page() has to be modified anyway, let's also make sure the mapped highmem pages are pinned with kmap_high_get() for the duration of the cache maintenance operation. Because kunmap() does unmap highmem pages lazily, it was reported by Gary King <GKing@nvidia.com> that those pages ended up being unmapped during cache maintenance on SMP causing segmentation faults. Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-12-14ARM: add size argument to __cpuc_flush_dcache_pageRussell King
... and rename the function since it no longer operates on just pages. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-10-11ARM: Add kmap_atomic type debuggingRussell King
Seemingly this support was missed when highmem was added, so DEBUG_HIGHMEM wouldn't have checked the kmap_atomic type. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-09-04ARM: 5691/1: fix cache aliasing issues between kmap() and kmap_atomic() with ↵Nicolas Pitre
highmem Let's suppose a highmem page is kmap'd with kmap(). A pkmap entry is used, the page mapped to it, and the virtual cache is dirtied. Then kunmap() is used which does virtually nothing except for decrementing a usage count. Then, let's suppose the _same_ page gets mapped using kmap_atomic(). It is therefore mapped onto a fixmap entry instead, which has a different virtual address unaware of the dirty cache data for that page sitting in the pkmap mapping. Fortunately it is easy to know if a pkmap mapping still exists for that page and use it directly with kmap_atomic(), thanks to kmap_high_get(). And actual testing with a printk in the added code path shows that this condition is actually met *extremely* frequently. Seems that we've been quite lucky that things have worked so well with highmem so far. Cc: stable@kernel.org Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-03-15[ARM] kmap supportNicolas Pitre
The kmap virtual area borrows a 2MB range at the top of the 16MB area below PAGE_OFFSET currently reserved for kernel modules and/or the XIP kernel. This 2MB corresponds to the range covered by 2 consecutive second-level page tables, or a single pmd entry as seen by the Linux page table abstraction. Because XIP kernels are unlikely to be seen on systems needing highmem support, there shouldn't be any shortage of VM space for modules (14 MB for modules is still way more than twice the typical usage). Because the virtual mapping of highmem pages can go away at any moment after kunmap() is called on them, we need to bypass the delayed cache flushing provided by flush_dcache_page() in that case. The atomic kmap versions are based on fixmaps, and __cpuc_flush_dcache_page() is used directly in that case. Signed-off-by: Nicolas Pitre <nico@marvell.com>