[PATCH v2 1/5] x86/shim: map and unmap page tables in replace_va_mapping

[Hongyan Xia <hx242@xxxxxxx>]

From: Wei Liu <wei.liu2@xxxxxxxxxx>

Also, introduce lYe_from_lXe() macros which do not rely on the direct
map when walking page tables. Unfortunately, they cannot be inline
functions due to the header dependency on domain_page.h, so keep them as
macros just like map_lYt_from_lXe().

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>

---
Changed in v2:
- unmap as early as possible instead of unmapping all at the end.
- use lYe_from_lXe() macros and lift them from a later patch to this
  patch.
- const qualify pointers in new macros.
---
 xen/arch/x86/pv/shim.c     |  9 +++++----
 xen/include/asm-x86/page.h | 13 +++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
index ed2ece8a8a..28d2076065 100644
--- a/xen/arch/x86/pv/shim.c
+++ b/xen/arch/x86/pv/shim.c
@@ -168,16 +168,17 @@ const struct platform_bad_page *__init 
pv_shim_reserved_pages(unsigned int *size
 static void __init replace_va_mapping(struct domain *d, l4_pgentry_t *l4start,
                                       unsigned long va, mfn_t mfn)
 {
-    l4_pgentry_t *pl4e = l4start + l4_table_offset(va);
-    l3_pgentry_t *pl3e = l4e_to_l3e(*pl4e) + l3_table_offset(va);
-    l2_pgentry_t *pl2e = l3e_to_l2e(*pl3e) + l2_table_offset(va);
-    l1_pgentry_t *pl1e = l2e_to_l1e(*pl2e) + l1_table_offset(va);
+    l4_pgentry_t l4e = l4start[l4_table_offset(va)];
+    l3_pgentry_t l3e = l3e_from_l4e(l4e, l3_table_offset(va));
+    l2_pgentry_t l2e = l2e_from_l3e(l3e, l2_table_offset(va));
+    l1_pgentry_t *pl1e = map_l1t_from_l2e(l2e) + l1_table_offset(va);
     struct page_info *page = mfn_to_page(l1e_get_mfn(*pl1e));
 
     put_page_and_type(page);
 
     *pl1e = l1e_from_mfn(mfn, (!is_pv_32bit_domain(d) ? L1_PROT
                                                       : COMPAT_L1_PROT));
+    UNMAP_DOMAIN_PAGE(pl1e);
 }
 
 static void evtchn_reserve(struct domain *d, unsigned int port)
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index c98d8f5ede..1e16f3980d 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -196,6 +196,19 @@ static inline l4_pgentry_t l4e_from_paddr(paddr_t pa, 
unsigned int flags)
 #define map_l2t_from_l3e(x)        (l2_pgentry_t 
*)map_domain_page(l3e_get_mfn(x))
 #define map_l3t_from_l4e(x)        (l3_pgentry_t 
*)map_domain_page(l4e_get_mfn(x))
 
+/* Unlike lYe_to_lXe(), lXe_from_lYe() do not rely on the direct map. */
+#define l2e_from_l3e(l3e, offset) ({                        \
+        const l2_pgentry_t *l2t = map_l2t_from_l3e(l3e);    \
+        l2_pgentry_t l2e = l2t[offset];                     \
+        UNMAP_DOMAIN_PAGE(l2t);                             \
+        l2e; })
+
+#define l3e_from_l4e(l4e, offset) ({                        \
+        const l3_pgentry_t *l3t = map_l3t_from_l4e(l4e);    \
+        l3_pgentry_t l3e = l3t[offset];                     \
+        UNMAP_DOMAIN_PAGE(l3t);                             \
+        l3e; })
+
 /* Given a virtual address, get an entry offset into a page table. */
 #define l1_table_offset(a)         \
     (((a) >> L1_PAGETABLE_SHIFT) & (L1_PAGETABLE_ENTRIES - 1))
-- 
2.24.1.AMZN