[Xen-changelog] [xen master] xen: arm: avoid unnecessary additional mappings in boot page tables.

[patchbot@xxxxxxx]

commit 37cc94f58cbd1ed26c85a92043e5c404c7dc17cc
Author:     Ian Campbell <ian.campbell@xxxxxxxxxx>
AuthorDate: Mon Jul 21 13:59:58 2014 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Thu Jul 24 16:23:17 2014 +0100

    xen: arm: avoid unnecessary additional mappings in boot page tables.
    
    If the identity map is created at one level then avoid creating
    entries further down the boot page tables, since these will be aliases at
    strange virtual address.
    
    For example consider an arm32 system (for simplicity) with Xen loaded at
    address 0x40402000. As a virtual address this corresponds to walking 
offsets 1,
    2 and 2 at the first, second and third levels respectively.
    
    When creating the identity map we will therefore create a 1GB super mapping 
at
    0x40000000 for the identity map, which is the one we want to use.
    
    However when considering the second level we will see the offset 2 and 
create a
    2MB mapping in slot 2 of boot_second. Since boot_second is mapped in slot 0 
of
    boot_first this corresponds to an unwanted mapping from virtual address
    0x00400000 to physical address 0x40400000.
    
    We still do not handle the case where the load address is within the 2MB 
range
    starting just after XEN_VIRT_START. This is not a regression but this patch
    tries to provide a more useful diagnostic message. We do handle loading at
    exactly XEN_VIRT_START.
    
    Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/arch/arm/arm32/head.S |   20 +++++++++++++++++---
 xen/arch/arm/arm64/head.S |   19 ++++++++++++++++---
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index a6ee342..0a95b68 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -45,7 +45,7 @@
  *   r3  -
  *   r4  -
  *   r5  -
- *   r6  -
+ *   r6  - identity map in place
  *   r7  - CPUID
  *   r8  - DTB address (boot CPU only)
  *   r9  - paddr(start)
@@ -250,6 +250,14 @@ cpu_init_done:
          * mapping. So each CPU must rebuild the page tables here with
          * the 1:1 in place. */
 
+        /* If Xen is loaded at exactly XEN_VIRT_START then we don't
+         * need an additional 1:1 mapping, the virtual mapping will
+         * suffice.
+         */
+        cmp   r9, #XEN_VIRT_START
+        moveq r6, #1                 /* r6 := identity map now in place */
+        movne r6, #0                 /* r6 := identity map not yet in place */
+
         /* Write Xen's PT's paddr into the HTTBR */
         ldr   r4, =boot_pgtable
         add   r4, r4, r10            /* r4 := paddr (boot_pagetable) */
@@ -275,6 +283,7 @@ cpu_init_done:
         orr   r2, r2, #PT_LOWER(MEM)
         lsl   r1, r1, #3             /* r1 := Slot offset */
         strd  r2, r3, [r4, r1]       /* Mapping of paddr(start) */
+        mov   r6, #1                 /* r6 := identity map now in place */
 
 1:      /* Setup boot_second: */
         ldr   r4, =boot_second
@@ -290,6 +299,8 @@ cpu_init_done:
         strd  r2, r3, [r4, #8]       /* Map it in slot 1 */
 
         /* ... map of paddr(start) in boot_second */
+        cmp   r6, #1                 /* r6 is set if already created */
+        beq   1f
         lsr   r2, r9, #SECOND_SHIFT  /* Offset of base paddr in boot_second */
         ldr   r3, =LPAE_ENTRY_MASK
         and   r1, r2, r3
@@ -302,6 +313,7 @@ cpu_init_done:
         mov   r3, #0x0
         lsl   r1, r1, #3             /* r1 := Slot offset */
         strd  r2, r3, [r4, r1]       /* Mapping of paddr(start) */
+        mov   r6, #1                 /* r6 := identity map now in place */
 
         /* Setup boot_third: */
 1:      ldr   r4, =boot_third
@@ -326,8 +338,10 @@ cpu_init_done:
 
         /* boot pagetable setup complete */
 
-        b     1f
-
+        cmp   r6, #1                /* Did we manage to create an identity 
mapping ? */
+        beq   1f
+        PRINT("Unable to build boot page tables - Failed to identity map 
Xen.\r\n")
+        b     fail
 virtphys_clash:
         /* Identity map clashes with boot_third, which we cannot handle yet */
         PRINT("- Unable to build boot page tables - virt and phys addresses 
clash. -\r\n")
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 99eb0a6..4f0ea2d 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -62,7 +62,7 @@
  *  x22 - is_secondary_cpu
  *  x23 - UART address
  *  x24 - cpuid
- *  x25 -
+ *  x25 - identity map in place
  *  x26 -
  *  x27 -
  *  x28 -
@@ -253,6 +253,13 @@ skip_bss:
          * mapping. So each CPU must rebuild the page tables here with
          * the 1:1 in place. */
 
+        /* If Xen is loaded at exactly XEN_VIRT_START then we don't
+         * need an additional 1:1 mapping, the virtual mapping will
+         * suffice.
+         */
+        cmp   x19, #XEN_VIRT_START
+        cset  x25, eq                /* x25 := identity map in place, or not */
+
         /* Write Xen's PT's paddr into TTBR0_EL2 */
         ldr   x4, =boot_pgtable
         add   x4, x4, x20            /* x4 := paddr (boot_pagetable) */
@@ -293,6 +300,7 @@ skip_bss:
         and   x1, x1, #LPAE_ENTRY_MASK /* x1 := Slot offset */
         lsl   x1, x1, #3
         str   x2, [x4, x1]           /* Mapping of paddr(start) */
+        mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_first: */
         ldr   x4, =boot_first        /* Next level into boot_first */
@@ -306,6 +314,7 @@ skip_bss:
         str   x2, [x4, #0]           /* Map it in slot 0 */
 
         /* ... map of paddr(start) in boot_first */
+        cbnz  x25, 1f                /* x25 is set if already created */
         lsr   x2, x19, #FIRST_SHIFT  /* x2 := Offset of base paddr in 
boot_first */
         and   x1, x2, #LPAE_ENTRY_MASK /* x1 := Slot to use */
         cbz   x1, 1f                 /* It's in slot 0, map in boot_second */
@@ -315,6 +324,7 @@ skip_bss:
         orr   x2, x2, x3
         lsl   x1, x1, #3             /* x1 := Slot offset */
         str   x2, [x4, x1]           /* Create mapping of paddr(start)*/
+        mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_second: */
         ldr   x4, =boot_second       /* Next level into boot_second */
@@ -328,6 +338,7 @@ skip_bss:
         str   x2, [x4, #8]           /* Map it in slot 1 */
 
         /* ... map of paddr(start) in boot_second */
+        cbnz  x25, 1f                /* x25 is set if already created */
         lsr   x2, x19, #SECOND_SHIFT /* x2 := Offset of base paddr in 
boot_second */
         and   x1, x2, #LPAE_ENTRY_MASK /* x1 := Slot to use */
         cmp   x1, #1
@@ -338,6 +349,7 @@ skip_bss:
         orr   x2, x2, x3
         lsl   x1, x1, #3             /* x1 := Slot offset */
         str   x2, [x4, x1]           /* Create mapping of paddr(start)*/
+        mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_third: */
         ldr   x4, =boot_third
@@ -361,8 +373,9 @@ skip_bss:
 
         /* boot pagetable setup complete */
 
-        b     1f
-
+        cbnz  x25, 1f                /* Did we manage to create an identity 
mapping ? */
+        PRINT("Unable to build boot page tables - Failed to identity map 
Xen.\r\n")
+        b     fail
 virtphys_clash:
         /* Identity map clashes with boot_third, which we cannot handle yet */
         PRINT("- Unable to build boot page tables - virt and phys addresses 
clash. -\r\n")
--
generated by git-patchbot for /home/xen/git/xen.git#master

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog