mm/cma: Cleanup highmem check

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.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 5 insertions, 10 deletions

diff --git a/mm/cma.c b/mm/cma.c
index c960459eda7e..94b3460cd608 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);
-#else
-        highmem_start = __pa(high_memory);
-#endif
+        highmem_start = __pa(high_memory - 1) + 1;
         pr_debug("%s(size %pa, base %pa, limit %pa alignment %pa)\n",
                 __func__, &size, &base, &limit, &alignment);