x86: re-introduce map_domain_page() et al

This is being done mostly in the form previously used on x86-32,
utilizing the second L3 page table slot within the per-domain mapping
area for those mappings. It remains to be determined whether that
concept is really suitable, or whether instead re-implementing at least
the non-global variant from scratch would be better.

Also add the helpers {clear,copy}_domain_page() as well as initial uses
of them.

One question is whether, to exercise the non-trivial code paths, we
shouldn't make the trivial shortcuts conditional upon NDEBUG being
defined. See the debugging patch at the end of the series.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

1 files changed, 2 insertions, 14 deletions

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index e043ba10b3..9627b076c6 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2661,9 +2661,6 @@ static inline int vcpumask_to_pcpumask(
     }
 }
 
-#define fixmap_domain_page(mfn) mfn_to_virt(mfn)
-#define fixunmap_domain_page(ptr) ((void)(ptr))
-
 long do_mmuext_op(
     XEN_GUEST_HANDLE_PARAM(mmuext_op_t) uops,
     unsigned int count,
@@ -2983,7 +2980,6 @@ long do_mmuext_op(
 
         case MMUEXT_CLEAR_PAGE: {
             struct page_info *page;
-            unsigned char *ptr;
 
             page = get_page_from_gfn(d, op.arg1.mfn, NULL, P2M_ALLOC);
             if ( !page || !get_page_type(page, PGT_writable_page) )
@@ -2998,9 +2994,7 @@ long do_mmuext_op(
             /* A page is dirtied when it's being cleared. */
             paging_mark_dirty(d, page_to_mfn(page));
 
-            ptr = fixmap_domain_page(page_to_mfn(page));
-            clear_page(ptr);
-            fixunmap_domain_page(ptr);
+            clear_domain_page(page_to_mfn(page));
 
             put_page_and_type(page);
             break;
@@ -3008,8 +3002,6 @@ long do_mmuext_op(
 
         case MMUEXT_COPY_PAGE:
         {
-            const unsigned char *src;
-            unsigned char *dst;
             struct page_info *src_page, *dst_page;
 
             src_page = get_page_from_gfn(d, op.arg2.src_mfn, NULL, P2M_ALLOC);
@@ -3034,11 +3026,7 @@ long do_mmuext_op(
             /* A page is dirtied when it's being copied to. */
             paging_mark_dirty(d, page_to_mfn(dst_page));
 
-            src = __map_domain_page(src_page);
-            dst = fixmap_domain_page(page_to_mfn(dst_page));
-            copy_page(dst, src);
-            fixunmap_domain_page(dst);
-            unmap_domain_page(src);
+            copy_domain_page(page_to_mfn(dst_page), page_to_mfn(src_page));
 
             put_page_and_type(dst_page);
             put_page(src_page);