[RFC][PATCH] arm64: Add support for CONFIG_DEBUG_VIRTUAL

[Laura Abbott]

x86 has an option CONFIG_DEBUG_VIRTUAL to do additional checks
on virt_to_phys calls. The goal is to catch users who are calling
virt_to_phys on non-linear addresses immediately. As features
such as CONFIG_VMAP_STACK get enabled for arm64, this becomes
increasingly important. Add checks to catch bad virt_to_phys
usage.

Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
---
This has been on my TODO list for a while. It caught a few bugs with
CONFIG_VMAP_STACK on x86 so when that eventually gets added
for arm64 it will be useful to have. This caught one driver calling __pa on an
ioremapped address already. RFC for a couple of reasons:

1) This is basically a direct port of the x86 approach.
2) I needed some #ifndef __ASSEMBLY__ which I don't like to throw around.
3) I'm not quite sure about the bounds check for the VIRTUAL_BUG_ON with KASLR,
specifically the _end check.
4) Is it worth actually keeping this as DEBUG_VIRTUAL vs. folding it into
another option?

---
 arch/arm64/include/asm/memory.h | 11 ++++++++++-
 arch/arm64/mm/Makefile          |  2 +-
 arch/arm64/mm/physaddr.c        | 17 +++++++++++++++++
 lib/Kconfig.debug               |  2 +-
 mm/cma.c                        |  2 +-
 5 files changed, 30 insertions(+), 4 deletions(-)
 create mode 100644 arch/arm64/mm/physaddr.c

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index ba62df8..9805adc 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -106,11 +106,19 @@
  * private definitions which should NOT be used outside memory.h
  * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
  */
-#define __virt_to_phys(x) ({						\
+#define __virt_to_phys_nodebug(x) ({					\
 	phys_addr_t __x = (phys_addr_t)(x);				\
 	__x & BIT(VA_BITS - 1) ? (__x & ~PAGE_OFFSET) + PHYS_OFFSET :	\
 				 (__x - kimage_voffset); })
 
+#ifdef CONFIG_DEBUG_VIRTUAL
+#ifndef __ASSEMBLY__
+extern unsigned long __virt_to_phys(unsigned long x);
+#endif
+#else
+#define __virt_to_phys(x)	__virt_to_phys_nodebug(x)
+#endif
+
 #define __phys_to_virt(x)	((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
 #define __phys_to_kimg(x)	((unsigned long)((x) + kimage_voffset))
 
@@ -202,6 +210,7 @@ static inline void *phys_to_virt(phys_addr_t x)
  * Drivers should NOT use these either.
  */
 #define __pa(x)			__virt_to_phys((unsigned long)(x))
+#define __pa_nodebug(x)		__virt_to_phys_nodebug((unsigned long)(x))
 #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
 #define virt_to_pfn(x)      __phys_to_pfn(__virt_to_phys(x))
diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
index 54bb209..bcea84e 100644
--- a/arch/arm64/mm/Makefile
+++ b/arch/arm64/mm/Makefile
@@ -5,6 +5,6 @@ obj-y				:= dma-mapping.o extable.o fault.o init.o \
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
 obj-$(CONFIG_ARM64_PTDUMP)	+= dump.o
 obj-$(CONFIG_NUMA)		+= numa.o
-
+obj-$(CONFIG_DEBUG_VIRTUAL)	+= physaddr.o
 obj-$(CONFIG_KASAN)		+= kasan_init.o
 KASAN_SANITIZE_kasan_init.o	:= n
diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
new file mode 100644
index 0000000..6c271e2
--- /dev/null
+++ b/arch/arm64/mm/physaddr.c
@@ -0,0 +1,17 @@
+#include <linux/mm.h>
+
+#include <asm/memory.h>
+
+unsigned long __virt_to_phys(unsigned long x)
+{
+	phys_addr_t __x = (phys_addr_t)x;
+
+	if (__x & BIT(VA_BITS - 1)) {
+		/* The bit check ensures this is the right range */
+		return (__x & ~PAGE_OFFSET) + PHYS_OFFSET;
+	} else {
+		VIRTUAL_BUG_ON(x < kimage_vaddr || x > (unsigned long)_end);
+		return (__x - kimage_voffset);
+	}
+}
+EXPORT_SYMBOL(__virt_to_phys);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 33bc56c..e5634bb 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -604,7 +604,7 @@ config DEBUG_VM_PGFLAGS
 
 config DEBUG_VIRTUAL
 	bool "Debug VM translations"
-	depends on DEBUG_KERNEL && X86
+	depends on DEBUG_KERNEL && (X86 || ARM64)
 	help
 	  Enable some costly sanity checks in virtual to page code. This can
 	  catch mistakes with virt_to_page() and friends.
diff --git a/mm/cma.c b/mm/cma.c
index 384c2cb..2345803 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -235,7 +235,7 @@ int __init cma_declare_contiguous(phys_addr_t base,
 	phys_addr_t highmem_start;
 	int ret = 0;
 
-#ifdef CONFIG_X86
+#if defined(CONFIG_X86) || defined(CONFIG_ARM64)
 	/*
 	 * high_memory isn't direct mapped memory so retrieving its physical
 	 * address isn't appropriate.  But it would be useful to check the
-- 
2.7.4