Re: x86-64 machine_to_phys vs NX bit

[Rik van Riel <riel@redhat.com>]

Keir Fraser wrote:
> On 24/8/06 8:25 pm, "Rik van Riel" <riel@redhat.com> wrote:
> 
>> Say, something like the following?
>>
>> -    paddr_t phys = mfn_to_pfn(machine >> PAGE_SHIFT);
>> +    paddr_t phys = mfn_to_pfn((machine >> PAGE_SHIFT) & PHYSICAL_MASK);
>>
>> I'm still thinking I may have missed something in the code
>> somewhere, but I've been looking at this for over an hour now
>> and can't seem to find it...
>>
>> Any ideas?
> 
> Your suggested patch looks reasonable but it'd be good to find out why this
> hasn't caused us problems. For example, perhaps supported_pte_mask doesn't
> include PAGE_NX, so we're never setting the NX bit on 64-bit PTEs?

We do set the NX bit.  Including on vmalloced pages...

> That must be worth checking out, possibly also tracing 
> machine_to_phys to find out where that bit 63 goes -- I agree that it
> looks like mfn_to_pfn() shouldn't work if bit63 is set in the
> 'maddr' argument.

Absolutely :)

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