Patch "arm64: vmemmap: use virtual projection of linear region" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

arm64: vmemmap: use virtual projection of linear region

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-vmemmap-use-virtual-projection-of-linear-region.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Fri, 26 Feb 2016 17:57:13 +0100
Subject: arm64: vmemmap: use virtual projection of linear region

From: Ard Biesheuvel <[email protected]>

commit dfd55ad85e4a7fbaa82df12467515ac3c81e8a3e upstream.

Commit dd006da21646 ("arm64: mm: increase VA range of identity map") made some changes to the memory mapping code to allow physical memory to reside at an offset that exceeds the size of the virtual mapping.

However, since the size of the vmemmap area is proportional to the size of the VA area, but it is populated relative to the physical space, we may end up with the struct page array being mapped outside of the vmemmap region. For instance, on my Seattle A0 box, I can see the following output in the dmesg log.

vmemmap : 0xffffffbdc0000000 - 0xffffffbfc0000000 ( 8 GB maximum)

             0xffffffbfc0000000 - 0xffffffbfd0000000   (   256 MB actual)

We can fix this by deciding that the vmemmap region is not a projection of the physical space, but of the virtual space above PAGE_OFFSET, i.e., the linear region. This way, we are guaranteed that the vmemmap region is of sufficient size, and we can even reduce the size by half.

---
 arch/arm64/include/asm/pgtable.h |    7 ++++---
 arch/arm64/mm/init.c             |    4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

@@ -34,13 +34,13 @@
 /*
  * VMALLOC and SPARSEMEM_VMEMMAP ranges.
  *
- * VMEMAP_SIZE: allows the whole VA space to be covered by a struct page array
+ * VMEMAP_SIZE: allows the whole linear region to be covered by a struct page array
  *	(rounded up to PUD_SIZE).
  * VMALLOC_START: beginning of the kernel VA space
  * VMALLOC_END: extends to the available space below vmmemmap, PCI I/O space,
  *	fixed mappings and modules
  */
-#define VMEMMAP_SIZE		ALIGN((1UL << (VA_BITS - PAGE_SHIFT)) * sizeof(struct page), PUD_SIZE)
+#define VMEMMAP_SIZE		ALIGN((1UL << (VA_BITS - PAGE_SHIFT - 1)) * sizeof(struct page), PUD_SIZE)
 
 #ifndef CONFIG_KASAN
 #define VMALLOC_START		(VA_START)

@@ -51,7 +51,8 @@
 
 #define VMALLOC_END		(PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
 
-#define vmemmap			((struct page *)(VMALLOC_END + SZ_64K))
+#define VMEMMAP_START		(VMALLOC_END + SZ_64K)
+#define vmemmap			((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
 
 #define FIRST_USER_ADDRESS	0UL
 

@@ -319,8 +319,8 @@ void __init mem_init(void)
 #endif
 		  MLG(VMALLOC_START, VMALLOC_END),
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
-		  MLG((unsigned long)vmemmap,
-		      (unsigned long)vmemmap + VMEMMAP_SIZE),
+		  MLG(VMEMMAP_START,
+		      VMEMMAP_START + VMEMMAP_SIZE),
 		  MLM((unsigned long)virt_to_page(PAGE_OFFSET),
 		      (unsigned long)virt_to_page(high_memory)),
 #endif

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arm64-vmemmap-use-virtual-projection-of-linear-region.patch