Re: [patch 1/5] mm: remap_vmalloc_range

[Andrew Morton <akpm@osdl.org>]

Nick Piggin <npiggin@suse.de> wrote:
>
> On Fri, Apr 21, 2006 at 12:17:12AM -0700, Andrew Morton wrote:
> > Nick Piggin <npiggin@suse.de> wrote:
> > >
> > > Add a remap_vmalloc_range and get rid of as many remap_pfn_range and
> > > vm_insert_page loops as possible.
> > > 
> > > remap_vmalloc_range can do a whole lot of nice range checking even
> > > if the caller gets it wrong (which it looks like one or two do).
> > > 
> > > 
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED)) {
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED)) {
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED)) {
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED))
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED)) {
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED)) {
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED))
> > > -		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED))
> > > -		if (remap_pfn_range(vma, start, page + vma->vm_pgoff,
> > > -						PAGE_SIZE, vma->vm_page_prot))
> > > -		if (remap_pfn_range(vma, addr, pfn, PAGE_SIZE, PAGE_READONLY))
> > 
> > You've removed the ability for the caller to set the pte protections - it
> > now always uses vma->vm_page_prot.
> > 
> > please explain...
> 
> They should use vma->vm_page_prot?
> 
> The callers affected are the PAGE_SHARED ones (the others are unchanged).
> Isn't it correct to provide readonly mappings if userspace asks for it?

Dunno.  I assume perfmon was using PAGE_READONLY because it doesn't want
userspace altering the memory.  One would think that this should be
enforced at mmap()-time, and that mprotect() might be able to override it
anyway.  But I haven't looked that closely.

First impression is that there's some potential for breaking stuff in all
this - convince me otherwise ;)

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