From 09ed3d5ba06137913960f9c9385f71fc384193ab Mon Sep 17 00:00:00 2001 From: Wei Liu Date: Sat, 15 Mar 2014 16:11:47 +0000 Subject: [PATCH] xen/balloon: flush persistent kmaps in correct position Xen balloon driver will update ballooned out pages' P2M entries to point to scratch page for PV guests. In 24f69373e2 ("xen/balloon: don't alloc page while non-preemptible", kmap_flush_unused was moved after updating P2M table. In that case for 32 bit PV guest we might end up with P2M X -----> S (S is mfn of balloon scratch page) M2P Y -----> X (Y is mfn in persistent kmap entry) kmap_flush_unused() iterates through all the PTEs in the kmap address space, using pte_to_page() to obtain the page. If the p2m and the m2p are inconsistent the incorrect page is returned. This will clear page->address on the wrong page which may cause subsequent oopses if that page is currently kmap'ed. Move the flush back between get_page and __set_phys_to_machine to fix this. Signed-off-by: Wei Liu Signed-off-by: David Vrabel Cc: stable@vger.kernel.org # 3.12+ --- drivers/xen/balloon.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 37d06ea624a..61a6ac8fa8f 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -399,11 +399,25 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) state = BP_EAGAIN; break; } + scrub_page(page); - pfn = page_to_pfn(page); - frame_list[i] = pfn_to_mfn(pfn); + frame_list[i] = page_to_pfn(page); + } - scrub_page(page); + /* + * Ensure that ballooned highmem pages don't have kmaps. + * + * Do this before changing the p2m as kmap_flush_unused() + * reads PTEs to obtain pages (and hence needs the original + * p2m entry). + */ + kmap_flush_unused(); + + /* Update direct mapping, invalidate P2M, and add to balloon. */ + for (i = 0; i < nr_pages; i++) { + pfn = frame_list[i]; + frame_list[i] = pfn_to_mfn(pfn); + page = pfn_to_page(pfn); #ifdef CONFIG_XEN_HAVE_PVMMU /* @@ -429,11 +443,9 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) } #endif - balloon_append(pfn_to_page(pfn)); + balloon_append(page); } - /* Ensure that ballooned highmem pages don't have kmaps. */ - kmap_flush_unused(); flush_tlb_all(); set_xen_guest_handle(reservation.extent_start, frame_list); -- 2.43.2