[PATCH v6 5/8] vmalloc: introduce remap_vmalloc_range_partial

[HATAYAMA Daisuke]

We want to allocate ELF note segment buffer on the 2nd kernel in
vmalloc space and remap it to user-space in order to reduce the risk
that memory allocation fails on system with huge number of CPUs and so
with huge ELF note segment that exceeds 11-order block size.

Although there's already remap_vmalloc_range for the purpose of
remapping vmalloc memory to user-space, we need to specify user-space
range via vma. Mmap on /proc/vmcore needs to remap range across
multiple objects, so the interface that requires vma to cover full
range is problematic.

This patch introduces remap_vmalloc_range_partial that receives
user-space range as a pair of base address and size and can be used
for mmap on /proc/vmcore case.

remap_vmalloc_range is rewritten using remap_vmalloc_range_partial.

Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
---

 include/linux/vmalloc.h |    4 +++
 mm/vmalloc.c            |   63 +++++++++++++++++++++++++++++++++--------------
 2 files changed, 48 insertions(+), 19 deletions(-)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 7d5773a..dd0a2c8 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -82,6 +82,10 @@ extern void *vmap(struct page **pages, unsigned int count,
 			unsigned long flags, pgprot_t prot);
 extern void vunmap(const void *addr);
 
+extern int remap_vmalloc_range_partial(struct vm_area_struct *vma,
+				       unsigned long uaddr, void *kaddr,
+				       unsigned long size);
+
 extern int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
 							unsigned long pgoff);
 void vmalloc_sync_all(void);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3875fa2..d9a9f4f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2148,42 +2148,44 @@ finished:
 }
 
 /**
- *	remap_vmalloc_range  -  map vmalloc pages to userspace
- *	@vma:		vma to cover (map full range of vma)
- *	@addr:		vmalloc memory
- *	@pgoff:		number of pages into addr before first page to map
+ *	remap_vmalloc_range_partial  -  map vmalloc pages to userspace
+ *	@vma:		vma to cover
+ *	@uaddr:		target user address to start at
+ *	@kaddr:		virtual address of vmalloc kernel memory
+ *	@size:		size of map area
  *
  *	Returns:	0 for success, -Exxx on failure
  *
- *	This function checks that addr is a valid vmalloc'ed area, and
- *	that it is big enough to cover the vma. Will return failure if
- *	that criteria isn't met.
+ *	This function checks that @kaddr is a valid vmalloc'ed area,
+ *	and that it is big enough to cover the range starting at
+ *	@uaddr in @vma. Will return failure if that criteria isn't
+ *	met.
  *
  *	Similar to remap_pfn_range() (see mm/memory.c)
  */
-int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
-						unsigned long pgoff)
+int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr,
+				void *kaddr, unsigned long size)
 {
 	struct vm_struct *area;
-	unsigned long uaddr = vma->vm_start;
-	unsigned long usize = vma->vm_end - vma->vm_start;
 
-	if ((PAGE_SIZE-1) & (unsigned long)addr)
+	size = PAGE_ALIGN(size);
+
+	if (((PAGE_SIZE-1) & (unsigned long)uaddr) ||
+	    ((PAGE_SIZE-1) & (unsigned long)kaddr))
 		return -EINVAL;
 
-	area = find_vm_area(addr);
+	area = find_vm_area(kaddr);
 	if (!area)
 		return -EINVAL;
 
 	if (!(area->flags & VM_USERMAP))
 		return -EINVAL;
 
-	if (usize + (pgoff << PAGE_SHIFT) > area->size - PAGE_SIZE)
+	if (kaddr + size > area->addr + area->size)
 		return -EINVAL;
 
-	addr += pgoff << PAGE_SHIFT;
 	do {
-		struct page *page = vmalloc_to_page(addr);
+		struct page *page = vmalloc_to_page(kaddr);
 		int ret;
 
 		ret = vm_insert_page(vma, uaddr, page);
@@ -2191,14 +2193,37 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
 			return ret;
 
 		uaddr += PAGE_SIZE;
-		addr += PAGE_SIZE;
-		usize -= PAGE_SIZE;
-	} while (usize > 0);
+		kaddr += PAGE_SIZE;
+		size -= PAGE_SIZE;
+	} while (size > 0);
 
 	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
 
 	return 0;
 }
+EXPORT_SYMBOL(remap_vmalloc_range_partial);
+
+/**
+ *	remap_vmalloc_range  -  map vmalloc pages to userspace
+ *	@vma:		vma to cover (map full range of vma)
+ *	@addr:		vmalloc memory
+ *	@pgoff:		number of pages into addr before first page to map
+ *
+ *	Returns:	0 for success, -Exxx on failure
+ *
+ *	This function checks that addr is a valid vmalloc'ed area, and
+ *	that it is big enough to cover the vma. Will return failure if
+ *	that criteria isn't met.
+ *
+ *	Similar to remap_pfn_range() (see mm/memory.c)
+ */
+int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
+						unsigned long pgoff)
+{
+	return remap_vmalloc_range_partial(vma, vma->vm_start,
+					   addr + (pgoff << PAGE_SHIFT),
+					   vma->vm_end - vma->vm_start);
+}
 EXPORT_SYMBOL(remap_vmalloc_range);
 
 /*