RE: [Xen-devel] [patch] nx bit shouldn't get set when disabled

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Keir Fraser wrote:
> On 8 Jun 2005, at 20:47, Scott Parish wrote:
> 
>>> Why does x86_64 get pte_mfn, but not pae i386? I think pci-dma.c
>>> should probably be shared between i386 and x86/64.
>> 
>> Last time i checked, the linux side of i386 pae wasn't merged into
>> bk, so i have nothing to test such a patch against. I'll plan on
>> getting a pae setup going again and sending a patch to gerd.
> 
> The functions that are changed aren't pae-specific, and they are
> already in the xen/i386 tree. They can be patched in anticipation of
> pae, even though they can only be properly tested non-pae for the time
> being. I'm not inclined to take patches for xen/x86_64/pci-dma.c
> anyway: I think we can patch the xen/i386 one and share it with
> xen/x86_64. Otherwise we're going to get unnecessary divergence
> between what really ought to be two identical files. (I already did
> this for arch/xen/i386/kernel/time.c, for example.)
> 
>>> Why the extra mask ops with __supported_pte_mask? Native x86/64
>>> builds obviously don't need them...
>> 
>> Definitions such as __PAGE_KERNEL set NX, but as Jun pointed out,
>> those should only be set when NX mode is enabled.
> 
> So the extra masking isn't required?
> 
>   -- Keir
Hold on.

Scott, in your patch:

-               pfn = pte->pte >> PAGE_SHIFT;
+               mfn = pte_mfn(*pte);

+#define pte_mfn(_pte) (((_pte).pte & PTE_MASK) >> PAGE_SHIFT)

These should not be necessary if pte is created correctly (w/ or w/o NX
bit depending on __supported_pte_mask) in the first place, as Keir
pointed out. That's what I meant by "We should fix the creator of the
pte (by __supported_pte_mask), not the consumer of it." And you always
cut off the NX bit in your patch.

So remove the changes to pci-dma.c and init.c. If that does not work,
move check_efer to right before pda_init(0) in x86_64_start_kernel() in
head64.c.

Jun
---
Intel Open Source Technology Center

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