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From: Ingo Molnar <>
To: Andi Kleen <>
Cc:,,, "H. Peter Anvin" <>
Subject: Re: [PATCH] Fix direct mapping correctly in ioremap
Date: Thu, 14 Feb 2008 17:03:23 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

* Andi Kleen <> 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.)

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


  reply	other threads:[~2008-02-14 16:03 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-14 11:59 [PATCH] Fix direct mapping correctly in ioremap Andi Kleen
2008-02-14 16:03 ` Ingo Molnar [this message]
2008-02-14 17:14   ` Andi Kleen

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