Messages in this thread | | | Date | Mon, 8 Apr 2013 15:53:31 +0100 | From | Andy Whitcroft <> | Subject | Re: x86/mm/pageattr: Code without effect? |
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On Sat, Apr 06, 2013 at 04:58:04PM +0200, Andrea Arcangeli wrote:
> You're right, so this location clearly didn't trigger the problem so I > didn't notice the noop here. I only exercised the fix in the other > locations of the file that had the same problem. > > It was a noop, so it really couldn't hurt but the below change should > activate the fix there too. On the same lines, there was a superfluous > initialization of new_prot too which I cleaned up.
Although the new code is essentially noop, the other part of the change in try_preserve_large_page() moves the canon_pgprot() up above the static_protections() incantation which replaces its value, thus we lose the effect of that on the protection bits. I suspect this only affects older CPUs (?) but I do think there is a negative semantic change here:
+ new_prot = canon_pgprot(new_prot); [...] new_prot = static_protections(req_prot, address, pfn); [...] - new_pte = pfn_pte(pte_pfn(old_pte), canon_pgprot(new_prot)); + new_pte = pfn_pte(pte_pfn(old_pte), new_prot);
-apw
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