[Xen-devel] [PATCH] x86/mm: switch to new APIs in arch_init_memory

[Hongyan Xia <hongyxia@xxxxxxxxxx>]

From: Wei Liu <wei.liu2@xxxxxxxxxx>

Since we now map and unmap Xen PTE pages, we would like to track the
lifetime of mappings so that 1) we do not dereference memory through a
variable after it is unmapped, 2) we do not unmap more than once.
Therefore, we introduce the UNMAP_DOMAIN_PAGE macro to nullify the
variable after unmapping, and ignore NULL in unmap_domain_page.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>
---
 xen/arch/x86/domain_page.c    |  2 +-
 xen/arch/x86/mm.c             | 14 ++++++++------
 xen/include/xen/domain_page.h |  5 +++++
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/domain_page.c b/xen/arch/x86/domain_page.c
index dd32712d2f..b03728e18e 100644
--- a/xen/arch/x86/domain_page.c
+++ b/xen/arch/x86/domain_page.c
@@ -181,7 +181,7 @@ void unmap_domain_page(const void *ptr)
     unsigned long va = (unsigned long)ptr, mfn, flags;
     struct vcpu_maphash_entry *hashent;
 
-    if ( va >= DIRECTMAP_VIRT_START )
+    if ( !va || va >= DIRECTMAP_VIRT_START )
         return;
 
     ASSERT(va >= MAPCACHE_VIRT_START && va < MAPCACHE_VIRT_END);
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 70b87c4830..9fcdcde5b7 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -356,19 +356,21 @@ void __init arch_init_memory(void)
             ASSERT(root_pgt_pv_xen_slots < ROOT_PAGETABLE_PV_XEN_SLOTS);
             if ( l4_table_offset(split_va) == l4_table_offset(split_va - 1) )
             {
-                l3_pgentry_t *l3tab = alloc_xen_pagetable();
+                mfn_t l3mfn = alloc_xen_pagetable_new();
 
-                if ( l3tab )
+                if ( !mfn_eq(l3mfn, INVALID_MFN) )
                 {
-                    const l3_pgentry_t *l3idle =
-                        l4e_to_l3e(idle_pg_table[l4_table_offset(split_va)]);
+                    l3_pgentry_t *l3idle = map_l3t_from_l4e(
+                            idle_pg_table[l4_table_offset(split_va)]);
+                    l3_pgentry_t *l3tab = map_domain_page(l3mfn);
 
                     for ( i = 0; i < l3_table_offset(split_va); ++i )
                         l3tab[i] = l3idle[i];
                     for ( ; i < L3_PAGETABLE_ENTRIES; ++i )
                         l3tab[i] = l3e_empty();
-                    split_l4e = l4e_from_mfn(virt_to_mfn(l3tab),
-                                             __PAGE_HYPERVISOR_RW);
+                    split_l4e = l4e_from_mfn(l3mfn, __PAGE_HYPERVISOR_RW);
+                    UNMAP_DOMAIN_PAGE(l3idle);
+                    UNMAP_DOMAIN_PAGE(l3tab);
                 }
                 else
                     ++root_pgt_pv_xen_slots;
diff --git a/xen/include/xen/domain_page.h b/xen/include/xen/domain_page.h
index 32669a3339..a182d33b67 100644
--- a/xen/include/xen/domain_page.h
+++ b/xen/include/xen/domain_page.h
@@ -72,4 +72,9 @@ static inline void unmap_domain_page_global(const void *va) 
{};
 
 #endif /* !CONFIG_DOMAIN_PAGE */
 
+#define UNMAP_DOMAIN_PAGE(p) do {   \
+    unmap_domain_page(p);           \
+    (p) = NULL;                     \
+} while ( false )
+
 #endif /* __XEN_DOMAIN_PAGE_H__ */
-- 
2.17.1


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