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Date: Mon, 12 Jun 2017 08:31:55 -0600
From: Tycho Andersen <tycho@...ker.com>
To: Laura Abbott <labbott@...hat.com>
Cc: linux-mm@...ck.org, Juerg Haefliger <juergh@...il.com>,
kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v4 3/3] xpfo: add support for hugepages
Hi Laura,
Thanks for taking a look.
On Fri, Jun 09, 2017 at 05:23:06PM -0700, Laura Abbott wrote:
> > - set_pte_atomic(pte, pfn_pte(page_to_pfn(page), canon_pgprot(prot)));
> > +
> > + BUG_ON(!pte);
> > +
> > + switch (level) {
> > + case PG_LEVEL_4K:
> > + set_pte_atomic(pte, pfn_pte(page_to_pfn(page), canon_pgprot(prot)));
> > + break;
> > + case PG_LEVEL_2M:
> > + case PG_LEVEL_1G: {
> > + struct cpa_data cpa;
> > + int do_split;
> > +
> > + memset(&cpa, 0, sizeof(cpa));
> > + cpa.vaddr = kaddr;
> > + cpa.pages = &page;
> > + cpa.mask_set = prot;
> > + pgprot_val(cpa.mask_clr) = ~pgprot_val(prot);
> > + cpa.numpages = 1;
> > + cpa.flags = 0;
> > + cpa.curpage = 0;
> > + cpa.force_split = 0;
> > +
> > + do_split = try_preserve_large_page(pte, (unsigned long)kaddr, &cpa);
> > + if (do_split < 0)
>
> I can't reproduce the failure you describe in the cover letter but are you sure this
> check is correct?
The check seems to only happen when splitting up a large page,
indicating that...
> It looks like try_preserve_large_page can return 1 on failure
> and you still need to call split_large_page.
...yes, you're absolutely right. When I fix this, it now fails to
boot, stalling on unpacking the initramfs. So it seems something else
is wrong too.
Cheers,
Tycho
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