x86: introduce a new set of APIs to manage Xen page tables

We are going to switch to using domheap page for page tables.
A new set of APIs is introduced to allocate and free pages of page
tables based on mfn instead of the xenheap direct map address. The
allocation and deallocation work on mfn_t but not page_info, because
they are required to work even before frame table is set up.

Implement the old functions with the new ones. We will rewrite, site
by site, other mm functions that manipulate page tables to use the new
APIs.

After the allocation, one needs to map and unmap via map_domain_page to
access the PTEs. This does not break xen half way, since the new APIs
still use xenheap pages underneath, and map_domain_page will just use
the directmap for mappings. They will be switched to use domheap and
dynamic mappings when usage of old APIs is eliminated.

No functional change intended in this patch.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Hongyan Xia <hongyxia@amazon.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Wei Liu <wl@xen.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index edc238e51a69cb4b494c0e449c7b8a459e99cd0a..70b87c483092943f0c8d10dbaef6cf377f36a2f4 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -120,6 +120,7 @@
 #include <xen/efi.h>
 #include <xen/grant_table.h>
 #include <xen/hypercall.h>
+#include <xen/mm.h>
 #include <asm/paging.h>
 #include <asm/shadow.h>
 #include <asm/page.h>
@@ -4944,22 +4945,43 @@ int mmcfg_intercept_write(
 }
 
 void *alloc_xen_pagetable(void)
+{
+    mfn_t mfn = alloc_xen_pagetable_new();
+
+    return mfn_eq(mfn, INVALID_MFN) ? NULL : mfn_to_virt(mfn_x(mfn));
+}
+
+void free_xen_pagetable(void *v)
+{
+    mfn_t mfn = v ? virt_to_mfn(v) : INVALID_MFN;
+
+    free_xen_pagetable_new(mfn);
+}
+
+/*
+ * For these PTE APIs, the caller must follow the alloc-map-unmap-free
+ * lifecycle, which means explicitly mapping the PTE pages before accessing
+ * them. The caller must check whether the allocation has succeeded, and only
+ * pass valid MFNs to map_domain_page().
+ */
+mfn_t alloc_xen_pagetable_new(void)
 {
     if ( system_state != SYS_STATE_early_boot )
     {
         void *ptr = alloc_xenheap_page();
 
         BUG_ON(!hardware_domain && !ptr);
-        return ptr;
+        return ptr ? virt_to_mfn(ptr) : INVALID_MFN;
     }
 
-    return mfn_to_virt(mfn_x(alloc_boot_pages(1, 1)));
+    return alloc_boot_pages(1, 1);
 }
 
-void free_xen_pagetable(void *v)
+/* mfn can be INVALID_MFN */
+void free_xen_pagetable_new(mfn_t mfn)
 {
-    if ( system_state != SYS_STATE_early_boot )
-        free_xenheap_page(v);
+    if ( system_state != SYS_STATE_early_boot && !mfn_eq(mfn, INVALID_MFN) )
+        free_xenheap_page(mfn_to_virt(mfn_x(mfn)));
 }
 
 static DEFINE_SPINLOCK(map_pgdir_lock);

diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index fafb3af46def063f550a9dc2d3c77fd5f5c9b8d4..a06b2fb81f6836ef3883cb2ef15ee6febf67d37f 100644 (file)
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -583,6 +583,9 @@ void *do_page_walk(struct vcpu *v, unsigned long addr);
 /* Allocator functions for Xen pagetables. */
 void *alloc_xen_pagetable(void);
 void free_xen_pagetable(void *v);
+mfn_t alloc_xen_pagetable_new(void);
+void free_xen_pagetable_new(mfn_t mfn);
+
 l1_pgentry_t *virt_to_xen_l1e(unsigned long v);
 
 int __sync_local_execstate(void);