[PATCHv2 2/6] mm/cma: Cleanup highmem check

From: Laura Abbott
Date: Wed Nov 02 2016 - 17:01:09 EST

6b101e2a3ce4 ("mm/CMA: fix boot regression due to physical address of
high_memory") added checks to use __pa_nodebug on x86 since
CONFIG_DEBUG_VIRTUAL complains about high_memory not being linearlly
mapped. arm64 is now getting support for CONFIG_DEBUG_VIRTUAL as well.
Rather than add an explosion of arches to the #ifdef, switch to an
alternate method to calculate the physical start of highmem using
the page before highmem starts. This avoids the need for the #ifdef and
extra __pa_nodebug calls.

Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
mm/cma.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 384c2cb..71a2ec1 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -235,18 +235,13 @@ int __init cma_declare_contiguous(phys_addr_t base,
phys_addr_t highmem_start;
int ret = 0;

-#ifdef CONFIG_X86
- * high_memory isn't direct mapped memory so retrieving its physical
- * address isn't appropriate. But it would be useful to check the
- * physical address of the highmem boundary so it's justifiable to get
- * the physical address from it. On x86 there is a validation check for
- * this case, so the following workaround is needed to avoid it.
+ * We can't use __pa(high_memory) directly, since high_memory
+ * isn't a valid direct map VA, and DEBUG_VIRTUAL will (validly)
+ * complain. Find the boundary by adding one to the last valid
+ * address.
- highmem_start = __pa_nodebug(high_memory);
- highmem_start = __pa(high_memory);
+ highmem_start = __pa(high_memory - 1) + 1;
pr_debug("%s(size %pa, base %pa, limit %pa alignment %pa)\n",
__func__, &size, &base, &limit, &alignment);