Messages in this thread Patch in this message |  | | | Date | Wed, 11 Jul 2012 18:48:02 +0100 | | From | Will Deacon <> | | Subject | Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace |
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On Tue, Jul 10, 2012 at 11:42:34AM +0100, Will Deacon wrote: > On Tue, Jul 10, 2012 at 10:45:13AM +0100, Will Deacon wrote: > > On Tue, Jul 10, 2012 at 12:57:14AM +0100, Hugh Dickins wrote: > > > If I start to grep the architectures for non-empty flush_dcache_page(), > > > I soon find things in arch/arm such as v4_mc_copy_user_highpage() doing > > > if (!test_and_set_bit(PG_dcache_clean,)) __flush_dcache_page() - where > > > the naming suggests that I'm right, it's the architecture's responsibility > > > to arrange whatever flushing is needed in its copy and clear page functions.
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> Ok, so this is exactly the problem. The hugetlb allocator uses its own > pool of huge pages, so free_huge_page followed by a later alloc_huge_page > will give you something where the page flags of the compound head do not > guarantee that PG_arch_1 is clear.
Just to confirm, the following quick hack at least results in the correct flushing for me (on ARM):
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e198831..7a7c9d3 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1141,6 +1141,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, } set_page_private(page, (unsigned long)spool); + clear_bit(PG_arch_1, &page->flags); vma_commit_reservation(h, vma, addr);
The question is whether we should tidy that up for the core code or get architectures to clear the bit in arch_make_huge_pte (which also seems to work).
Will
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