Re: [PATCH v2 7/8] powerpc/fsl_booke: make sure PAGE_OFFSET map to memstart_addr for relocatable kernel

On Fri, Jul 26, 2013 at 07:17:57PM -0500, Scott Wood wrote:

On 07/04/2013 07:54:13 AM, Kevin Hao wrote:

quoted

@@ -1222,6 +1266,9 @@ _GLOBAL(switch_to_as1)

/*
 * Restore to the address space 0 and also invalidate the tlb
entry created
 * by switch_to_as1.
+ * r3 - the tlb entry which should be invalidated
+ * r4 - __pa(PAGE_OFFSET in AS0) - pa(PAGE_OFFSET in AS1)
+ * r5 - device tree virtual address
*/
_GLOBAL(restore_to_as0)
	mflr	r0

@@ -1230,7 +1277,15 @@ _GLOBAL(restore_to_as0)

0:	mflr	r9
	addi	r9,r9,1f - 0b

-	mfmsr	r7
+	/*
+	 * We may map the PAGE_OFFSET in AS0 to a different physical
address,
+	 * so we need calculate the right jump and device tree address
based
+	 * on the offset passed by r4.
+	*/

Whitespace

Fixed.

quoted

+	subf	r9,r4,r9
+	subf	r5,r4,r5
+
+2:	mfmsr	r7
	li	r8,(MSR_IS | MSR_DS)
	andc	r7,r7,r8

@@ -1249,9 +1304,19 @@ _GLOBAL(restore_to_as0)

	mtspr	SPRN_MAS1,r9
	tlbwe
	isync
+
+	cmpwi	r4,0
+	bne	3f
	mtlr	r0
	blr

+	/*
+	 * The PAGE_OFFSET will map to a different physical address,
+	 * jump to _start to do another relocation again.
+	*/
+3:	mr	r3,r5
+	bl	_start
+
/*
 * We put a few things here that have to be page-aligned. This stuff
 * goes at the beginning of the data segment, which is page-aligned.

diff --git a/arch/powerpc/mm/fsl_booke_mmu.c

b/arch/powerpc/mm/fsl_booke_mmu.c
index 8f60ef8..dd283fd 100644

--- a/arch/powerpc/mm/fsl_booke_mmu.c
+++ b/arch/powerpc/mm/fsl_booke_mmu.c

@@ -224,7 +224,7 @@ void __init adjust_total_lowmem(void)

	i = switch_to_as1();
	__max_low_memory = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM);
-	restore_to_as0(i);
+	restore_to_as0(i, 0, 0);

The device tree virtual address is zero?

No. But if the __pa(PAGE_OFFSET in AS0) is equal to __pa(PAGE_OFFSET in AS1),
that mean we don't need to do another relocation and the device tree virtual
address is useless in this case.

quoted

	pr_info("Memory CAM mapping: ");
	for (i = 0; i < tlbcam_index - 1; i++)

@@ -245,30 +245,56 @@ void setup_initial_memory_limit(phys_addr_t

first_memblock_base,
}

#ifdef CONFIG_RELOCATABLE
-notrace void __init relocate_init(phys_addr_t start)
+int __initdata is_second_reloc;
+notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
{
	unsigned long base = KERNELBASE;

-	/*
-	 * Relocatable kernel support based on processing of dynamic
-	 * relocation entries.
-	 * Compute the virt_phys_offset :
-	 * virt_phys_offset = stext.run - kernstart_addr
-	 *
-	 * stext.run = (KERNELBASE & ~0xfffffff) + (kernstart_addr &
0xfffffff)
-	 * When we relocate, we have :
-	 *
-	 *	(kernstart_addr & 0xfffffff) = (stext.run & 0xfffffff)
-	 *
-	 * hence:
-	 *  virt_phys_offset = (KERNELBASE & ~0xfffffff) -
-	 *                              (kernstart_addr & ~0xfffffff)
-	 *
-	 */
	kernstart_addr = start;
-	start &= ~0xfffffff;
-	base &= ~0xfffffff;
-	virt_phys_offset = base - start;
+	if (!is_second_reloc) {

Since it's at the end of a function and one side is much shorter
than the
other, please do:

	if (is_second_reloc) {
		virt_phys_offset = PAGE_OFFSET - memstart_addr;
		return;
	}

	/* the rest of the code goes here without having to indent
everything */

Yes, this looks much better. Changed.

Otherwise, please use positive logic for if/else constructs.

quoted

+		phys_addr_t size;
+
+		/*
+		 * Relocatable kernel support based on processing of dynamic
+		 * relocation entries. Before we get the real memstart_addr,
+		 * We will compute the virt_phys_offset like this:
+		 * virt_phys_offset = stext.run - kernstart_addr
+		 *
+		 * stext.run = (KERNELBASE & ~0xfffffff) +
+		 *				(kernstart_addr & 0xfffffff)
+		 * When we relocate, we have :
+		 *
+		 *	(kernstart_addr & 0xfffffff) = (stext.run & 0xfffffff)
+		 *
+		 * hence:
+		 *  virt_phys_offset = (KERNELBASE & ~0xfffffff) -
+		 *                              (kernstart_addr & ~0xfffffff)
+		 *
+		 */
+		start &= ~0xfffffff;
+		base &= ~0xfffffff;
+		virt_phys_offset = base - start;
+		early_get_first_memblock_info(__va(dt_ptr), &size);
+		/*
+		 * We now get the memstart_addr, then we should check if this
+		 * address is the same as what the PAGE_OFFSET map to now. If
+		 * not we have to change the map of PAGE_OFFSET to
memstart_addr
+		 * and do a second relocation.
+		 */
+		if (start != memstart_addr) {
+			unsigned long ram;
+			int n, offset = memstart_addr - start;
+
+			is_second_reloc = 1;
+			ram = size;
+			n = switch_to_as1();
+			map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM);

Do we really need this much RAM mapped at this point?

Not really.

 Why can't we
continue
with the same size TLB entry that we've been using, until the second
relocation?

OK, I will change it to use 64M.

quoted

+			restore_to_as0(n, offset, __va(dt_ptr));
+			/* We should never reach here */
+			panic("Relocation error");

Where is execution supposed to resume?  It looks like you're
expecting it
to resume from _start,

Yes.

but why?

For second relocation, we need to:
  * do the real relocate
  * set the interrupt vector
  * zero the BSS

So starting from the _start will avoid to duplicate these codes.

 And where is this effect of
restore_to_as0() documented?

There is a comment about this in restore_to_as0.

        /*   
         * The PAGE_OFFSET will map to a different physical address,
         * jump to _start to do another relocation again.
        */
3:      mr      r3,r5
        bl      _start

Thanks,
Kevin

-Scott