Re: [PATCH] Fix direct mapping correctly in ioremap

Andi Kleen
2008-02-14T16:38:30Z

On Thu, Feb 14, 2008 at 05:03:23PM +0100, Ingo Molnar wrote:
>
> * Andi Kleen <andi@firstfloor.org> wrote:
>
> > - if (ioremap_change_attr(vaddr, size, mode) < 0) {
> > + /* Fix up the direct mapping for the new cache attributes */
> > + err = ioremap_change_attr((unsigned long)__va(phys_addr),
> > + size + offset, mode);
>
> Ugh. This would break the 32-bit kernel - if any phys_addr larger than
> 1GB is passed in (which is the common case on 32-bit) then we'll start
> changing the attributes of random (most likely user-space) pages!
> That is because on 32-bit __va() does this:
>
> #define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
>
> where on 32-bit 3GB:1GB split PAGE_OFFSET is defined to 0xc0000000.
>
> So if a driver passes in the physical address of a PCI device with a BAR
> at 0xe1000000 somewhere in the PCI aperture, we'll get
> 0xe1000000+0xc0000000 == 0x91000000 - right in the middle of user-space.
>
> Changing attributes there is very wrong. (it could even crash the kernel
> in certain circumstances.)

True. It needs a end_pfn_map check. I'll revise.

> Have you tried to boot this patch on 32-bit? There are a couple of new

Yes, it booted on several machines. Don't think I saw CPA messages,
but i might have missed them.

> safety nets in the cpa code that would/should trigger very visibly -
> such as the warning here:
>
> if (!pte_val(old_pte)) {
> printk(KERN_WARNING "CPA: called for zero pte. "
> "vaddr = %lx cpa->vaddr = %lx\n", address,
> cpa->vaddr);
> WARN_ON(1);
> return -EINVAL;
> }
>
> (these are already there in -git)
>
> Please have a look at how we solved the "secondary alias" 64-bit problem
> in x86.git#mm and please resend against x86.git#mm if you still think
> something is missing. Thanks,

I want this regression fixed in .25, so #mm is not an option for this.

-Andi