Subject: arm64: kernel panic in paging_init()

From: [email-masked] (Catalin Marinas)
Date: Tue, 4 Feb 2014 12:14:52 +0000

On Mon, Feb 03, 2014 at 08:50:49PM +0000, Mark Salter wrote:
> I'm seeing the following panic in paging init. This is on the foundation
> model with a modified dtb memory node which has a non section-aligned
> bank:
> 	memory at 80000000 {
> 		device_type = "memory";
> 		reg = <0x00000000 0x80000000 0 0x20000000>,
> 		      <0x00000000 0xa0300000 0 0x1fd00000>;
> 	};
> 
> I only see this with 64k pagesize configured. What happens is the
> non section-aligned bank causes alloc_init_pte() to allocate a page
> for the new pte from the end of the first bank (the failing address
> 0xfffffe001fff0000 [0x9fff0000 phys]). This should be a valid page
> since it was mapped during the create_mapping() call for the first
> memory bank. A flush_tlb_all() added to the end of create_mapping()
> makes the panic go away so I think the problem is something stale
> cached before the page with the failing address was mapped.

I think it goes like this:

head.S maps enough memory to get started but using 64K pages rather than
512M sections with a single pgd entry and several ptes. This never gets
to the end of the first block (just up to KERNEL_END).

create_mapping() realises it can do a 512M section mapping, overriding
the original table pgd entry with a block one. The memblock limit is set
correctly PGDIR_SIZE but create_mapping, when it replaces the table pgd
with a block one doesn't do any TLB invalidation.

So I wouldn't do a TLB invalidation all the time but only when the old
pmd was set. Please give the patch below a try, I only compiled it (I'll
add some text afterwards):

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index f557ebbe7013..f8dc7e8fce6f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -203,10 +203,18 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
 	do {
 		next = pmd_addr_end(addr, end);
 		/* try section mapping first */
-		if (((addr | next | phys) & ~SECTION_MASK) == 0)
+		if (((addr | next | phys) & ~SECTION_MASK) == 0) {
+			pmd_t old_pmd =*pmd;
 			set_pmd(pmd, __pmd(phys | prot_sect_kernel));
-		else
+			/*
+			 * Check for previous table entries created during
+			 * boot (__create_page_tables) and flush them.
+			 */
+			if (!pmd_none(old_pmd))
+				flush_tlb_all();
+		} else {
 			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys));
+		}
 		phys += next - addr;
 	} while (pmd++, addr = next, addr != end);
 }

Thanks.

-- 
Catalin