On Fri, Jun 24, 2005 at 01:20:04PM -0500, [email protected] wrote:
> Rik Van Riel wrote:
> > On Wed, 22 Jun 2005 [email protected] wrote:
> >
> >> My question is this: when split_large_page() is called, should it
> >> make the other 511 PTEs inherit the page attributes from the large
> >> page (with the exception of PAGE_PSE, obviously)?
> >
> > I suspect it should.
>
> (Copying Andi Kleen & Andrea Arcangeli since they were involved in a
> previous discussion of this. I'm trying to fix the NX handling when
> change_page_attr() is called in i386.)
>
> After looking into it further, I agree completely. I found a thread in
> which this was discussed
> (http://marc.theaimsgroup.com/?l=linux-kernel&m=109964359124731&w=2),
> and discovered that this has been addressed in the X86_64 kernel.
You don't say which kernel you were working against. 2.6.11 has
some fixes in this area (in particular with the reference counts)
> However, when I used "change_page_attr()" to change the page to
> PAGE_KERNEL, it did just that. But PAGE_KERNEL has the _PAGE_NX bit set
> and isn't executable. And, since PAGE_KERNEL (with _PAGE_NX set) didn't
> match the original pages attributes, the 512 PTEs weren't reverted back
> into a large page. (Also, __change_page_attr() did *another* get_page()
> on the page containing these 512 PTEs, so now the page_count has gone up
> to 3, instead of going back down to 1 (or staying at 2).)
That should be already fixed.
>
> Is the function that calls "change_page_attr()" expected to look at the
> attributes of the page before calling change_page_attr(), so it knows
> how to un-change the attributes when it is finished with the page (since
> PAGE_KERNEL isn't always what the page was originally)?
No, it's not supposed to do such checks on its own.
>
> Or should "change_page_attr()" ignore the NX bit in the "pgprot_t prot"
> parameter that's passed to it, and just inherit NX from the
> large/existing page? Then change_page_attr(page,PAGE_KERNEL) could be
> used to undo changes, but change_page_attr() couldn't be used to modify
> the NX bit.
I don't think that makes sense. It should exactly set the protection
the caller requested and revert when the protection is exactly like
it was before.
-Andi
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
