[GIT PULL] memremap fix for 4.3

[Williams, Dan J]

Hi Linus, please pull from:

  git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-fixes

...to receive a small fixlet for 4.3.

The new memremap() api introduced in the 4.3 cycle to unify/replace
ioremap_cache() and ioremap_wt() is mishandling the highmem case.  This
patch has received a build success notification from a 0day-kbuild-robot
run and has been out for a review for a day.  Russell has not had a
chance to weigh in on it yet.

I do not think the usage of kmap is strictly necessary as we should be
able to fall back to ioremap_cache(), but I include it for two reasons:

1/ ARM ioremap() will WARN if passed a pfn_valid() address.

2/ acpi_map() carries a similar kmap fallback, and that quirk can now be
centrally carried in this common routine.


---

The following changes since commit 25cb62b76430a91cc6195f902e61c2cb84ade622:

  Linux 4.3-rc5 (2015-10-11 11:09:45 -0700)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-fixes

for you to fetch changes up to bcaa4236b558092dd5ff14ea943e89fd944fcd28:

  memremap: fix highmem support (2015-10-26 16:55:56 -0400)

----------------------------------------------------------------
Dan Williams (1):
      memremap: fix highmem support

 include/linux/highmem.h | 12 ++++++++++++
 kernel/memremap.c       | 28 +++++++++++++++++++++++++---
 2 files changed, 37 insertions(+), 3 deletions(-)

commit bcaa4236b558092dd5ff14ea943e89fd944fcd28
Author: Dan Williams <dan.j.williams at intel.com>
Date:   Mon Oct 26 16:55:56 2015 -0400

    memremap: fix highmem support
    
    Currently memremap checks if the range is "System RAM" and returns the
    kernel linear address.  This is broken for highmem platforms where a
    range may be "System RAM", but is not part of the kernel linear mapping.
    Similar to acpi_map(), use kmap() for PAGE_SIZE memremap() requests for
    highmem, and fall back to ioremap_cache() otherwise.
    
    The impact of this bug is low for now since the pmem driver is the only
    user of memremap(), but this is important to fix before more conversions
    to memremap arrive in 4.4.
    
    Cc: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
    Reported-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
    Signed-off-by: Dan Williams <dan.j.williams at intel.com>

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 6aefcd0031a6..c20cf24c76dd 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -41,6 +41,13 @@ void kmap_flush_unused(void);
 
 struct page *kmap_to_page(void *addr);
 
+static inline bool is_kmap_addr(const void *x)
+{
+	unsigned long addr = (unsigned long) x;
+
+	return addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP);
+}
+
 #else /* CONFIG_HIGHMEM */
 
 static inline unsigned int nr_free_highpages(void) { return 0; }
@@ -50,6 +57,11 @@ static inline struct page *kmap_to_page(void *addr)
 	return virt_to_page(addr);
 }
 
+static inline bool is_kmap_addr(const void *x)
+{
+	return false;
+}
+
 #define totalhigh_pages 0UL
 
 #ifndef ARCH_HAS_KMAP
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 72b0c66628b6..901d7ec3583a 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -10,6 +10,7 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  */
+#include <linux/highmem.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/io.h>
@@ -24,6 +25,25 @@ __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size)
 }
 #endif
 
+static void *try_ram_remap(resource_size_t offset, size_t size)
+{
+	struct page *page = pfn_to_page(offset >> PAGE_SHIFT);
+	unsigned int pg_off = offset & ~PAGE_MASK;
+
+	/* In the simple case just return the existing linear address */
+	if (!PageHighMem(page))
+		return __va(offset);
+
+	/*
+	 * Try kmap first since some arch ioremap implementations fail when
+	 * being passed a ram address.
+	 */
+	if (pg_off + size <= PAGE_SIZE)
+		return kmap(page) + pg_off;
+
+	return NULL;
+}
+
 /**
  * memremap() - remap an iomem_resource as cacheable memory
  * @offset: iomem resource start address
@@ -66,8 +86,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
 		 * the requested range is potentially in "System RAM"
 		 */
 		if (is_ram == REGION_INTERSECTS)
-			addr = __va(offset);
-		else
+			addr = try_ram_remap(offset, size);
+		if (!addr)
 			addr = ioremap_cache(offset, size);
 	}
 
@@ -94,7 +114,9 @@ EXPORT_SYMBOL(memremap);
 
 void memunmap(void *addr)
 {
-	if (is_vmalloc_addr(addr))
+	if (is_kmap_addr(addr))
+		kunmap(addr);
+	else if (is_vmalloc_addr(addr))
 		iounmap((void __iomem *) addr);
 }
 EXPORT_SYMBOL(memunmap);