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Commit fb155c16 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Allow arbitrary shared PFNMAP's 



A shared mapping doesn't cause COW-pages, so we don't need to worry
about the whole vm_pgoff logic to decide if a PFN-remapped page has
gone through COW or not.

This makes it possible to entirely avoid the special "partial remapping"
logic for the common case.

Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e4f5c82a

mm/memory.c

+12 −4
Original line number Diff line number Diff line
@@ -377,6 +377,8 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_ 
		unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;

		if (pfn == vma->vm_pgoff + off)

			return NULL;

		if (vma->vm_flags & VM_SHARED)

			return NULL;

	}



	/*
@@ -1343,9 +1345,6 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, 
	struct mm_struct *mm = vma->vm_mm;

	int err;



	if (addr != vma->vm_start || end != vma->vm_end)

		return incomplete_pfn_remap(vma, addr, end, pfn, prot);



	/*

	 * Physically remapped pages are special. Tell the

	 * rest of the world about it:
@@ -1359,9 +1358,18 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, 
	 *   VM_PFNMAP tells the core MM that the base pages are just

	 *	raw PFN mappings, and do not have a "struct page" associated

	 *	with them.

	 *

	 * There's a horrible special case to handle copy-on-write

	 * behaviour that some programs depend on. We mark the "original"

	 * un-COW'ed pages by matching them up with "vma->vm_pgoff".

	 */

	vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;

	if (!(vma->vm_flags & VM_SHARED)) {

		if (addr != vma->vm_start || end != vma->vm_end)

			return incomplete_pfn_remap(vma, addr, end, pfn, prot);

		vma->vm_pgoff = pfn;

	}



	vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;



	BUG_ON(addr >= end);

	pfn -= addr >> PAGE_SHIFT;