[RFC PATCH 5/9] ARM64: mm: Add support for flushing huge pages.
From: Will Deacon <hidden>
Date: 2013-05-01 11:05:41
Also in:
linux-arch, linux-mm
Hi Steve, On Tue, Apr 30, 2013 at 05:30:44PM +0100, Steve Capper wrote:
quoted hunk ↗ jump to hunk
The code to flush the dcache of a dirty page, __flush_dcache_page, will only flush the head of a HugeTLB/THP page. This patch adjusts __flush_dcache_page such that the order of the compound page is used to determine the size of area to flush. Signed-off-by: Steve Capper <redacted> --- arch/arm64/mm/flush.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c index 88611c3..71c182d 100644 --- a/arch/arm64/mm/flush.c +++ b/arch/arm64/mm/flush.c@@ -72,7 +72,8 @@ void copy_to_user_page(struct vm_area_struct *vma, struct page *page, void __flush_dcache_page(struct page *page) { - __flush_dcache_area(page_address(page), PAGE_SIZE); + size_t page_size = PAGE_SIZE << compound_order(page); + __flush_dcache_area(page_address(page), page_size); }
This penalises flush_dcache_page, while it might only be required for __sync_icache_dcache (called when installing executable ptes). Now, the job of flush_dcache_page is to deal with D-side aliases between concurrent user and kernel mappings. On arm64, D-side aliasing is not a problem so in theory flush_dcache_page could be a nop (well, a clear_bit, but close enough). The reason that flush_dcache_page *isn't* currently a nop, is because we have harvard caches, so if we end up in a situation where the kernel is writing executable text to a page which is also mapped into userspace (i.e. there won't be a subsequent call to set_pte), then the user will execute junk if we don't flush/invalidate things here. This might be overkill. I can't think of a scenario where the above is true, but I'm no mm expert, so it would be great if somebody else could chime in to confirm/rubbish out suspicions... Cheers, Will