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authorAlexey Kardashevskiy <aik@ozlabs.ru>2013-08-28 18:37:42 +1000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-10-11 17:24:39 +1100
commit8e0861fa3c4edfc2f30dd4cf4d58d3929f7c1b23 (patch)
tree07a0b749245da2e29918d9f2121d7ca68e9b2763 /include/linux/page-flags.h
parent81fcfb813fe99c30f77dd3ed9a4e541d14a9ed01 (diff)
powerpc: Prepare to support kernel handling of IOMMU map/unmap
The current VFIO-on-POWER implementation supports only user mode driven mapping, i.e. QEMU is sending requests to map/unmap pages. However this approach is really slow, so we want to move that to KVM. Since H_PUT_TCE can be extremely performance sensitive (especially with network adapters where each packet needs to be mapped/unmapped) we chose to implement that as a "fast" hypercall directly in "real mode" (processor still in the guest context but MMU off). To be able to do that, we need to provide some facilities to access the struct page count within that real mode environment as things like the sparsemem vmemmap mappings aren't accessible. This adds an API function realmode_pfn_to_page() to get page struct when MMU is off. This adds to MM a new function put_page_unless_one() which drops a page if counter is bigger than 1. It is going to be used when MMU is off (for example, real mode on PPC64) and we want to make sure that page release will not happen in real mode as it may crash the kernel in a horrible way. CONFIG_SPARSEMEM_VMEMMAP and CONFIG_FLATMEM are supported. Cc: linux-mm@kvack.org Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'include/linux/page-flags.h')
-rw-r--r--include/linux/page-flags.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 6d53675c2b54..98ada58f9942 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -329,7 +329,9 @@ static inline void set_page_writeback(struct page *page)
* System with lots of page flags available. This allows separate
* flags for PageHead() and PageTail() checks of compound pages so that bit
* tests can be used in performance sensitive paths. PageCompound is
- * generally not used in hot code paths.
+ * generally not used in hot code paths except arch/powerpc/mm/init_64.c
+ * and arch/powerpc/kvm/book3s_64_vio_hv.c which use it to detect huge pages
+ * and avoid handling those in real mode.
*/
__PAGEFLAG(Head, head) CLEARPAGEFLAG(Head, head)
__PAGEFLAG(Tail, tail)