[Xen-changelog] [mini-os master] minios: don't rely on specific page table allocation scheme

[patchbot@xxxxxxx]

commit 8d84345a20d8a46ea26379c9f19961f6aa3e6e83
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Fri Nov 20 19:32:42 2015 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Mon Nov 23 09:38:58 2015 +0000

    minios: don't rely on specific page table allocation scheme
    
    Today mini-os is making assumptions how the page tables it is started
    with are being allocated. Especially it is using the number of page
    table frames to calculate which is the first unmapped pfn.
    
    Instead of relying on page table number assumptions just look into the
    page tables to find the first pfn not already mapped.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
---
 arch/x86/mm.c         |   93 +++++++++++--------------------------------------
 include/x86/arch_mm.h |    7 ----
 2 files changed, 21 insertions(+), 79 deletions(-)

diff --git a/arch/x86/mm.c b/arch/x86/mm.c
index 186659d..51aa966 100644
--- a/arch/x86/mm.c
+++ b/arch/x86/mm.c
@@ -132,61 +132,6 @@ static void new_pt_frame(unsigned long *pt_pfn, unsigned 
long prev_l_mfn,
 }
 
 /*
- * Checks if a pagetable frame is needed at 'level' to map a given
- * address. Note, this function is specific to the initial page table
- * building.
- */
-static int need_pt_frame(unsigned long va, int level)
-{
-    unsigned long hyp_virt_start = HYPERVISOR_VIRT_START;
-#if defined(__x86_64__)
-    unsigned long hyp_virt_end = HYPERVISOR_VIRT_END;
-#else
-    unsigned long hyp_virt_end = 0xffffffff;
-#endif
-
-    /* In general frames will _not_ be needed if they were already
-       allocated to map the hypervisor into our VA space */
-#if defined(__x86_64__)
-    if ( level == L3_FRAME )
-    {
-        if ( l4_table_offset(va) >= 
-             l4_table_offset(hyp_virt_start) &&
-             l4_table_offset(va) <= 
-             l4_table_offset(hyp_virt_end))
-            return 0;
-        return 1;
-    } 
-    else
-#endif
-
-    if ( level == L2_FRAME )
-    {
-#if defined(__x86_64__)
-        if ( l4_table_offset(va) >= 
-             l4_table_offset(hyp_virt_start) &&
-             l4_table_offset(va) <= 
-             l4_table_offset(hyp_virt_end))
-#endif
-            if ( l3_table_offset(va) >= 
-                 l3_table_offset(hyp_virt_start) &&
-                 l3_table_offset(va) <= 
-                 l3_table_offset(hyp_virt_end))
-                return 0;
-
-        return 1;
-    } 
-    else 
-        /* Always need l1 frames */
-        if ( level == L1_FRAME )
-            return 1;
-
-    printk("ERROR: Unknown frame level %d, hypervisor %lx,%lx\n", 
-           level, hyp_virt_start, hyp_virt_end);
-    return -1;
-}
-
-/*
  * Build the initial pagetable.
  */
 static void build_pagetable(unsigned long *start_pfn, unsigned long *max_pfn)
@@ -200,8 +145,9 @@ static void build_pagetable(unsigned long *start_pfn, 
unsigned long *max_pfn)
     int count = 0;
     int rc;
 
-    pfn_to_map = 
-        (start_info.nr_pt_frames - NOT_L1_FRAMES) * L1_PAGETABLE_ENTRIES;
+    /* Be conservative: even if we know there will be more pages already
+       mapped, start the loop at the very beginning. */
+    pfn_to_map = *start_pfn;
 
     if ( *max_pfn >= virt_to_pfn(HYPERVISOR_VIRT_START) )
     {
@@ -229,9 +175,8 @@ static void build_pagetable(unsigned long *start_pfn, 
unsigned long *max_pfn)
 #if defined(__x86_64__)
         offset = l4_table_offset(start_address);
         /* Need new L3 pt frame */
-        if ( !(start_address & L3_MASK) )
-            if ( need_pt_frame(start_address, L3_FRAME) ) 
-                new_pt_frame(&pt_pfn, pt_mfn, offset, L3_FRAME);
+        if ( !(tab[offset] & _PAGE_PRESENT) )
+            new_pt_frame(&pt_pfn, pt_mfn, offset, L3_FRAME);
 
         page = tab[offset];
         pt_mfn = pte_to_mfn(page);
@@ -239,29 +184,33 @@ static void build_pagetable(unsigned long *start_pfn, 
unsigned long *max_pfn)
 #endif
         offset = l3_table_offset(start_address);
         /* Need new L2 pt frame */
-        if ( !(start_address & L2_MASK) )
-            if ( need_pt_frame(start_address, L2_FRAME) )
-                new_pt_frame(&pt_pfn, pt_mfn, offset, L2_FRAME);
+        if ( !(tab[offset] & _PAGE_PRESENT) )
+            new_pt_frame(&pt_pfn, pt_mfn, offset, L2_FRAME);
 
         page = tab[offset];
         pt_mfn = pte_to_mfn(page);
         tab = to_virt(mfn_to_pfn(pt_mfn) << PAGE_SHIFT);
         offset = l2_table_offset(start_address);        
         /* Need new L1 pt frame */
-        if ( !(start_address & L1_MASK) )
-            if ( need_pt_frame(start_address, L1_FRAME) )
-                new_pt_frame(&pt_pfn, pt_mfn, offset, L1_FRAME);
+        if ( !(tab[offset] & _PAGE_PRESENT) )
+            new_pt_frame(&pt_pfn, pt_mfn, offset, L1_FRAME);
 
         page = tab[offset];
         pt_mfn = pte_to_mfn(page);
+        tab = to_virt(mfn_to_pfn(pt_mfn) << PAGE_SHIFT);
         offset = l1_table_offset(start_address);
 
-        mmu_updates[count].ptr =
-            ((pgentry_t)pt_mfn << PAGE_SHIFT) + sizeof(pgentry_t) * offset;
-        mmu_updates[count].val = 
-            (pgentry_t)pfn_to_mfn(pfn_to_map++) << PAGE_SHIFT | L1_PROT;
-        count++;
-        if ( count == L1_PAGETABLE_ENTRIES || pfn_to_map == *max_pfn )
+        if ( !(tab[offset] & _PAGE_PRESENT) )
+        {
+            mmu_updates[count].ptr =
+                ((pgentry_t)pt_mfn << PAGE_SHIFT) + sizeof(pgentry_t) * offset;
+            mmu_updates[count].val =
+                (pgentry_t)pfn_to_mfn(pfn_to_map) << PAGE_SHIFT | L1_PROT;
+            count++;
+        }
+        pfn_to_map++;
+        if ( count == L1_PAGETABLE_ENTRIES ||
+             (count && pfn_to_map == *max_pfn) )
         {
             rc = HYPERVISOR_mmu_update(mmu_updates, count, NULL, DOMID_SELF);
             if ( rc < 0 )
diff --git a/include/x86/arch_mm.h b/include/x86/arch_mm.h
index 23cfca7..58f29fc 100644
--- a/include/x86/arch_mm.h
+++ b/include/x86/arch_mm.h
@@ -56,12 +56,6 @@
 
 #define L2_MASK  ((1UL << L3_PAGETABLE_SHIFT) - 1)
 
-/*
- * If starting from virtual address greater than 0xc0000000,
- * this value will be 2 to account for final mid-level page
- * directory which is always mapped in at this location.
- */
-#define NOT_L1_FRAMES           3
 #define PRIpte "016llx"
 #ifndef __ASSEMBLY__
 typedef uint64_t pgentry_t;
@@ -87,7 +81,6 @@ typedef uint64_t pgentry_t;
 #define L2_MASK  ((1UL << L3_PAGETABLE_SHIFT) - 1)
 #define L3_MASK  ((1UL << L4_PAGETABLE_SHIFT) - 1)
 
-#define NOT_L1_FRAMES           3
 #define PRIpte "016lx"
 #ifndef __ASSEMBLY__
 typedef unsigned long pgentry_t;
--
generated by git-patchbot for /home/xen/git/mini-os.git#master

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