[PATCH v3 21/21] vmcore: introduce mmap_vmcore()

[HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>]

This patch introduces mmap_vmcore().

If flag MEM_TYPE_CURRENT_KERNEL is set, remapped is the buffer on the
2nd kernel. If not set, remapped is some area in old memory.

Neither writable nor executable mapping is permitted even with
mprotect(). Non-writable mapping is also requirement of
remap_pfn_range() when mapping linear pages on non-consequtive
physical pages; see is_cow_mapping().

On x86-32 PAE kernels, mmap() supports at most 16TB memory only. This
limitation comes from the fact that the third argument of
remap_pfn_range(), pfn, is of 32-bit length on x86-32: unsigned long.

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

 fs/proc/vmcore.c |   72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 72 insertions(+), 0 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index dd1d601..bc4848c 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -185,9 +185,81 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
 	return acc;
 }
 
+static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
+{
+	size_t size = vma->vm_end - vma->vm_start;
+	u64 start, end, len, tsz;
+	struct vmcore *m;
+
+	if (!support_mmap_vmcore)
+		return -ENODEV;
+
+	start = (u64)vma->vm_pgoff << PAGE_SHIFT;
+	end = start + size;
+
+	if (size > vmcore_size || end > vmcore_size)
+		return -EINVAL;
+
+	if (vma->vm_flags & (VM_WRITE | VM_EXEC))
+		return -EPERM;
+
+	vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC);
+
+	len = 0;
+
+	if (start < elfcorebuf_sz) {
+		u64 pfn;
+
+		tsz = elfcorebuf_sz - start;
+		if (size < tsz)
+			tsz = size;
+		pfn = __pa(elfcorebuf + start) >> PAGE_SHIFT;
+		if (remap_pfn_range(vma, vma->vm_start, pfn, tsz,
+				    vma->vm_page_prot))
+			return -EAGAIN;
+		size -= tsz;
+		start += tsz;
+		len += tsz;
+
+		if (size == 0)
+			return 0;
+	}
+
+	list_for_each_entry(m, &vmcore_list, list) {
+		if (start < m->offset + m->size) {
+			u64 pfn = 0;
+
+			tsz = m->offset + m->size - start;
+			if (size < tsz)
+				tsz = size;
+			if (m->flag & MEM_TYPE_CURRENT_KERNEL) {
+				pfn = __pa(m->buf + start - m->offset)
+					>> PAGE_SHIFT;
+			} else {
+				pfn = (m->paddr + (start - m->offset))
+					>> PAGE_SHIFT;
+			}
+			if (remap_pfn_range(vma, vma->vm_start + len, pfn, tsz,
+					    vma->vm_page_prot)) {
+				do_munmap(vma->vm_mm, vma->vm_start, len);
+				return -EAGAIN;
+			}
+			size -= tsz;
+			start += tsz;
+			len += tsz;
+
+			if (size == 0)
+				return 0;
+		}
+	}
+
+	return 0;
+}
+
 static const struct file_operations proc_vmcore_operations = {
 	.read		= read_vmcore,
 	.llseek		= default_llseek,
+	.mmap		= mmap_vmcore,
 };
 
 static struct vmcore* __init get_new_element(void)