Re: [RESEND] Question about recursive mappings

[Mathieu Ropert <mro@adviseo.fr>]

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Keir Fraser wrote:

>
> On 24 May 2006, at 21:12, Mathieu Ropert wrote:
>
>> Ok, i've done a little patch which seems to resolve the issue on my 
>> test setup. Basically, i've modified get_linear_pagetable(), added a 
>> level parameter and call it for each level but level 1.
>> I need to do a little more test before i post the patch. As tomorrow 
>> is a national day, it should be ready friday.
>
>
> Can you try creating some mutually recursive pagetables (i.e., one 
> linearly maps the other, and vice versa) and then try 'xm destroy'ing 
> the domain?
>
>  -- Keir
>
Here's the patch that solves my issue. I've only tested it for x86_64, 
so any feedback on x86/PAE would be appreciated.
Tried to make mutually recursive tables and destroy the domain as you 
suggested, no problem encountered.
Note that the union i used may seem a bit overkill, but i didn't saw any 
other way to make it generic (even if brutal casting should work on any 
x86/x86_64 arch).
Applies to cset 10166.

Mathieu

Signed-off-by: Mathieu Ropert <mro@adviseo.fr>



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diff -u -r a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c	2006-05-26 11:05:08.000000000 +0200
+++ b/xen/arch/x86/mm.c	2006-05-26 11:14:33.000000000 +0200
@@ -415,7 +415,7 @@
  */
 static int 
 get_linear_pagetable(
-    root_pgentry_t re, unsigned long re_pfn, struct domain *d)
+    pgentry_t re, unsigned long re_pfn, struct domain *d, int level)
 {
     unsigned long x, y;
     struct page_info *page;
@@ -423,13 +423,13 @@
 
     ASSERT( !shadow_mode_refcounts(d) );
 
-    if ( (root_get_flags(re) & _PAGE_RW) )
+    if ( (pgentry_get_flags(re, level) & _PAGE_RW) )
     {
         MEM_LOG("Attempt to create linear p.t. with write perms");
         return 0;
     }
 
-    if ( (pfn = root_get_pfn(re)) != re_pfn )
+    if ( (pfn = pgentry_get_pfn(re, level)) != re_pfn )
     {
         /* Make sure the mapped frame belongs to the correct domain. */
         if ( unlikely(!get_page_from_pagenr(pfn, d)) )
@@ -444,8 +444,7 @@
         do {
             x = y;
             if ( unlikely((x & PGT_count_mask) == PGT_count_mask) ||
-                 unlikely((x & (PGT_type_mask|PGT_validated)) != 
-                          (PGT_root_page_table|PGT_validated)) )
+                 unlikely(!(x & PGT_validated) || !is_ptp(x)))
             {
                 put_page(page);
                 return 0;
@@ -532,9 +531,12 @@
     vaddr <<= PGT_va_shift;
     rc = get_page_and_type_from_pagenr(
         l2e_get_pfn(l2e), PGT_l1_page_table | vaddr, d);
-#if CONFIG_PAGING_LEVELS == 2
-    if ( unlikely(!rc) )
-        rc = get_linear_pagetable(l2e, pfn, d);
+#if CONFIG_PAGING_LEVELS >= 2
+    if ( unlikely(!rc) ) {
+        pgentry_t re;
+        re.l2.l2 = l2e.l2;
+        rc = get_linear_pagetable(re, pfn, d, 2);
+    }
 #endif
     return rc;
 }
@@ -564,9 +566,12 @@
     rc = get_page_and_type_from_pagenr(
         l3e_get_pfn(l3e),
         PGT_l2_page_table | vaddr, d);
-#if CONFIG_PAGING_LEVELS == 3
-    if ( unlikely(!rc) )
-        rc = get_linear_pagetable(l3e, pfn, d);
+#if CONFIG_PAGING_LEVELS >= 3
+    if ( unlikely(!rc) ) {
+        pgentry_t re;
+        re.l3.l3 = l3e.l3;
+        rc = get_linear_pagetable(re, pfn, d, 3);
+    }
 #endif
     return rc;
 }
@@ -597,8 +602,11 @@
         l4e_get_pfn(l4e), 
         PGT_l3_page_table | vaddr, d);
 
-    if ( unlikely(!rc) )
-        rc = get_linear_pagetable(l4e, pfn, d);
+    if ( unlikely(!rc) ) {
+        pgentry_t re;
+        re.l4.l4 = l4e.l4;
+        rc = get_linear_pagetable(re, pfn, d, 4);
+    }	
 
     return rc;
 }
diff -u -r a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
--- a/xen/include/asm-x86/page.h	2006-05-26 11:05:09.000000000 +0200
+++ b/xen/include/asm-x86/page.h	2006-05-24 12:49:42.000000000 +0200
@@ -176,6 +176,67 @@
 #define pagetable_get_pfn(x)   ((x).pfn)
 #define mk_pagetable(pa)       \
     ({ pagetable_t __p; __p.pfn = (pa) >> PAGE_SHIFT; __p; })
+
+typedef union {
+    l1_pgentry_t l1;
+#if CONFIG_PAGING_LEVELS >= 2
+    l2_pgentry_t l2;
+#if CONFIG_PAGING_LEVELS >= 3
+    l3_pgentry_t l3;
+#if CONFIG_PAGING_LEVELS == 4
+    l4_pgentry_t l4;
+#endif	/* LEVELS == 4 */
+#endif	/* LEVELS >= 3 */
+#endif	/* LEVELS >= 2 */
+} pgentry_t;
+
+static inline intpte_t pgentry_get_flags(pgentry_t p, int level)
+{
+    switch (level)
+    {
+    case 1:
+        return l1e_get_flags(p.l1);
+#if CONFIG_PAGING_LEVELS >= 2
+    case 2:
+        return l2e_get_flags(p.l2);
+#if CONFIG_PAGING_LEVELS >= 3
+    case 3:
+        return l3e_get_flags(p.l3);
+#if CONFIG_PAGING_LEVELS == 4
+    case 4:
+        return l4e_get_flags(p.l4);
+#endif	/* LEVELS == 4 */
+#endif	/* LEVELS >= 3 */
+#endif	/* LEVELS >= 2 */
+    default:
+        /* should not happen */
+        return 0;
+    }
+}
+
+static inline intpte_t pgentry_get_pfn(pgentry_t p, int level)
+{
+    switch (level)
+    {
+    case 1:
+        return l1e_get_pfn(p.l1);
+#if CONFIG_PAGING_LEVELS >= 2
+    case 2:
+        return l2e_get_pfn(p.l2);
+#if CONFIG_PAGING_LEVELS >= 3
+    case 3:
+        return l3e_get_pfn(p.l3);
+#if CONFIG_PAGING_LEVELS == 4
+    case 4:
+        return l4e_get_pfn(p.l4);
+#endif	/* LEVELS == 4 */
+#endif	/* LEVELS >= 3 */
+#endif	/* LEVELS >= 2 */
+    default:
+        /* should not happen */
+        return 0;
+    }
+}
 #endif
 
 #define clear_page(_p)      memset((void *)(_p), 0, PAGE_SIZE)
diff -u -r a/xen/include/asm-x86/x86_32/page-2level.h b/xen/include/asm-x86/x86_32/page-2level.h
--- a/xen/include/asm-x86/x86_32/page-2level.h	2006-05-26 11:05:09.000000000 +0200
+++ b/xen/include/asm-x86/x86_32/page-2level.h	2006-05-26 11:09:56.000000000 +0200
@@ -28,6 +28,11 @@
 
 #endif /* !__ASSEMBLY__ */
 
+/* Check if page type is page table (any level) */
+#define is_ptp(x)                                   \
+        ((x & PGT_type_mask) == PGT_l1_page_table   \
+        || (x & PGT_type_mask) == PGT_l2_page_table)
+
 /* root table */
 #define root_get_pfn              l2e_get_pfn
 #define root_get_flags            l2e_get_flags
diff -u -r a/xen/include/asm-x86/x86_32/page-3level.h b/xen/include/asm-x86/x86_32/page-3level.h
--- a/xen/include/asm-x86/x86_32/page-3level.h	2006-05-26 11:05:09.000000000 +0200
+++ b/xen/include/asm-x86/x86_32/page-3level.h	2006-05-26 11:10:47.000000000 +0200
@@ -38,6 +38,12 @@
 
 #endif /* !__ASSEMBLY__ */
 
+/* Check if page type is page table (any level) */
+#define is_ptp(x)                                   \
+        ((x & PGT_type_mask) == PGT_l1_page_table   \
+        || (x & PGT_type_mask) == PGT_l2_page_table \
+        || (x & PGT_type_mask) == PGT_l3_page_table)
+
 /* root table */
 #define root_get_pfn              l3e_get_pfn
 #define root_get_flags            l3e_get_flags
diff -u -r a/xen/include/asm-x86/x86_64/page.h b/xen/include/asm-x86/x86_64/page.h
--- a/xen/include/asm-x86/x86_64/page.h	2006-05-26 11:05:09.000000000 +0200
+++ b/xen/include/asm-x86/x86_64/page.h	2006-05-26 11:07:46.000000000 +0200
@@ -41,6 +41,13 @@
 
 #endif /* !__ASSEMBLY__ */
 
+/* Check if page type is page table (any level) */
+#define is_ptp(x)                                   \
+        ((x & PGT_type_mask) == PGT_l1_page_table   \
+        || (x & PGT_type_mask) == PGT_l2_page_table \
+        || (x & PGT_type_mask) == PGT_l3_page_table \
+        || (x & PGT_type_mask) == PGT_l4_page_table)
+
 /* Given a virtual address, get an entry offset into a linear page table. */
 #define l1_linear_offset(_a) (((_a) & VADDR_MASK) >> L1_PAGETABLE_SHIFT)
 #define l2_linear_offset(_a) (((_a) & VADDR_MASK) >> L2_PAGETABLE_SHIFT)

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