From c497bfa63390db9d2242c1ae2dfbee2a000e7ece Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Fri, 27 Dec 2019 10:01:43 +0100 Subject: [PATCH] x86/mm: avoid IOMMU operations in more cases in _get_page_type() All that really matters is whether writability of a page changes; in particular e.g. page table -> page table (but different levels) transitions do not require unmapping the page from the IOMMU again. Note that the XSA-288 fix did arrange for PGT_none pages not needing special consideration here. Signed-off-by: Jan Beulich Acked-by: Andrew Cooper --- xen/arch/x86/mm.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 594f1bd290..b48777cc19 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -2980,17 +2980,19 @@ static int _get_page_type(struct page_info *page, unsigned long type, return -EINTR; } - if ( unlikely((x & PGT_type_mask) != type) ) + if ( unlikely(((x & PGT_type_mask) == PGT_writable_page) != + (type == PGT_writable_page)) ) { /* Special pages should not be accessible from devices. */ struct domain *d = page_get_owner(page); + if ( d && is_pv_domain(d) && unlikely(need_iommu_pt_sync(d)) ) { mfn_t mfn = page_to_mfn(page); if ( (x & PGT_type_mask) == PGT_writable_page ) rc = iommu_legacy_unmap(d, _dfn(mfn_x(mfn)), PAGE_ORDER_4K); - else if ( type == PGT_writable_page ) + else rc = iommu_legacy_map(d, _dfn(mfn_x(mfn)), mfn, PAGE_ORDER_4K, IOMMUF_readable | IOMMUF_writable); -- 2.30.2