[PATCH] mm/CMA: fix boot regression due to physical address of high_memory

[Joonsoo Kim]

high_memory isn't direct mapped memory so retrieving it's physical
address isn't appropriate. But, it would be useful to check physical
address of highmem boundary so it's justfiable to get physical address
from it. In x86, there is a validation check if CONFIG_DEBUG_VIRTUAL
and it triggers following boot failure reported by Ingo.

...
BUG: Int 6: CR2 00f06f53
     EDI   (null)  ESI 0665b000  EBP c1ed7edc  EBX 40000000
     ESP c1ed7ed8   ES 0000007b   DS 0000007b
     EDX c2022c18  ECX 37d34000  EAX   (null)
     vec 00000006  err   (null)  EIP c102b62e   CS 00000060  flg 00210013
...
Call Trace:
 [<c1902dfd>] dump_stack+0x41/0x52
 [<c1fad1f7>] early_idt_handler+0x6b/0x6b
 [<c102b62e>] ? __phys_addr+0x16/0x68
 [<c1fccd26>] cma_declare_contiguous+0x33/0x212
 [<c1fe9b6e>] dma_contiguous_reserve_area+0x31/0x4e
 [<c1fe9ca8>] dma_contiguous_reserve+0x11d/0x125
 [<c1faf2c8>] ? setup_real_mode+0x98/0xa3
 [<c1fb00c8>] setup_arch+0x7b5/0xb63
 [<c1fad802>] start_kernel+0xb8/0x3e6
 [<c1fad2cb>] i386_start_kernel+0x79/0x7d

To fix boot regression, this patch implements workaround to avoid
validation check in x86 when retrieving physical address of high_memory.
__pa_nodebug() used by this patch is implemented only in x86 so
there is no choice but to use dirty #ifdef.

Reported-by: Ingo Molnar <mingo@xxxxxxxxxx>
Tested-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/cma.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index ee3c3e0..35c4787 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -227,9 +227,22 @@ int __init cma_declare_contiguous(phys_addr_t base,
 			bool fixed, struct cma **res_cma)
 {
 	phys_addr_t memblock_end = memblock_end_of_DRAM();
-	phys_addr_t highmem_start = __pa(high_memory);
+	phys_addr_t highmem_start;
 	int ret = 0;
 
+#ifdef CONFIG_X86
+	/*
+	 * high_memory isn't direct mapped memory so retrieving it's
+	 * physical address isn't appropriate. But, it would be useful
+	 * to check physical address of highmem boundary so it's
+	 * justfiable to get physical address from it. In x86, there is
+	 * a validation check for this case, so following workaround is
+	 * needed to avoid it.
+	 */
+	highmem_start = __pa_nodebug(high_memory);
+#else
+	highmem_start = __pa(high_memory);
+#endif
 	pr_debug("%s(size %pa, base %pa, limit %pa alignment %pa)\n",
 		__func__, &size, &base, &limit, &alignment);
 
-- 
1.7.9.5

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