Re: [Xen-devel] [PATCH 4/7] arm: map device tree blob in initial page tables

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 03/02/12 21:18, Tim Deegan wrote:
> At 19:15 +0000 on 03 Feb (1328296512), David Vrabel wrote:
>> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>>
>> Add a 1:1 mapping for the device tree blob in the initial page tables.
>> This will allow the DTB to be parsed for memory information prior to
>> setting up the real page tables.
>>
>> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
>> ---
>>  xen/arch/arm/head.S |    5 +++++
>>  1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/xen/arch/arm/head.S b/xen/arch/arm/head.S
>> index 9951f37..8385481 100644
>> --- a/xen/arch/arm/head.S
>> +++ b/xen/arch/arm/head.S
>> @@ -202,6 +202,11 @@ hyp:
>>      add   r4, r4, #8
>>      strd  r2, r3, [r1, r4]       /* Map it in the fixmap's slot */
>>  #endif
>> +    mov   r3, #0x0
>> +    orr   r2, r8, #0xe00
>> +    orr   r2, r2, #0x07d
>> +    mov   r4, r8, lsr #18        /* Slot for (r8 == atag_paddr) */
>> +    strd  r2, r3, [r1, r4]       /* Map DTB there */
> 
> It might be better to map the DTB at a fixed VA (say, the next
> second-level slot up from the fixmap one) so we don't have to worry
> about the DTB's PA clashing with Xen's VAs.

That was already used in setup_pagetables() to relocate Xen but since
the two uses don't overlap they can share the same slot.  Not 100% sure
on the TLB flush after updating the L2 PTE -- it makes it work but is it
sufficient/optimal?

8<-------
arm: map device tree blob in initial page tables

Add a mapping for the device tree blob in the initial page tables.
This will allow the DTB to be parsed for memory information prior to
setting up the real page tables.

It is mapped into the first L2 slot after the fixmap.  When this slot
is reused in setup_pagetables(), flush the TLB.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 xen/arch/arm/head.S          |    7 +++++++
 xen/arch/arm/mm.c            |    5 +++--
 xen/include/asm-arm/config.h |    6 ++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/head.S b/xen/arch/arm/head.S
index 3c1f624..f1a81b3 100644
--- a/xen/arch/arm/head.S
+++ b/xen/arch/arm/head.S
@@ -201,6 +201,13 @@ hyp:
         add   r4, r4, #8
         strd  r2, r3, [r1, r4]       /* Map it in the fixmap's slot */
 #endif
+        mov   r3, #0x0
+        lsr   r2, r8, #21
+        lsl   r2, r2, #21            /* 2MB-aligned paddr of DTB */
+        orr   r2, r2, #0xf00
+        orr   r2, r2, #0x07d         /* r2:r3 := 2MB RAM incl. DTB */
+        add   r4, r4, #8
+        strd  r2, r3, [r1, r4]       /* Map it in the early boot slot */

         PRINT("- Turning on paging -\r\n")

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 613d084..0599102 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -161,10 +161,11 @@ void __init setup_pagetables(unsigned long
boot_phys_offset)

     xen_paddr = XEN_PADDR;

-    /* Map the destination in the empty L2 above the fixmap */
-    dest_va = FIXMAP_ADDR(0) + (1u << SECOND_SHIFT);
+    /* Map the destination in the boot misc area. */
+    dest_va = BOOT_MISC_VIRT_START;
     pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT);
     write_pte(xen_second + second_table_offset(dest_va), pte);
+    flush_xen_data_tlb();

     /* Calculate virt-to-phys offset for the new location */
     phys_offset = xen_paddr - (unsigned long) _start;
diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
index 12285dd..8546a50 100644
--- a/xen/include/asm-arm/config.h
+++ b/xen/include/asm-arm/config.h
@@ -52,15 +52,21 @@
  *  0  -   2M   Unmapped
  *  2M -   4M   Xen text, data, bss
  *  4M -   6M   Fixmap: special-purpose 4K mapping slots
+ *  6M  -  8M   Early boot misc (see below)
  *
  * 32M - 128M   Frametable: 24 bytes per page for 16GB of RAM
  *
  *  1G -   2G   Xenheap: always-mapped memory
  *  2G -   4G   Domheap: on-demand-mapped
+ *
+ * The early boot misc area is used:
+ *   - in head.S for the DTB for device_tree_early_init().
+ *   - in setup_pagetables() when relocating Xen.
  */

 #define XEN_VIRT_START         0x00200000
 #define FIXMAP_ADDR(n)        (0x00400000 + (n) * PAGE_SIZE)
+#define BOOT_MISC_VIRT_START   0x00600000
 #define FRAMETABLE_VIRT_START  0x02000000
 #define XENHEAP_VIRT_START     0x40000000
 #define DOMHEAP_VIRT_START     0x80000000

David

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