Regular oops on shutdown of KVM/ARM64 machines with VGA device

[Catalin Marinas]

On Wed, Jul 01, 2015 at 09:20:28AM +0100, Marc Zyngier wrote:
> [+Will, Catalin]
> 
> On 30/06/15 19:50, Christoffer Dall wrote:
> > On Tue, Jun 30, 2015 at 05:20:11PM +0100, Marc Zyngier wrote:
> >> On 30/06/15 17:16, Dirk Müller wrote:
> >>> Hi Marc,
> >>>
> >>>> Can try the following patch?
> >>>
> >>> [..]
> >>>
> >>> Thanks a lot for the quick patch, from a brief testing this seems to
> >>> fix the issue (on a 4k kernel). I'll retest this in our original
> >>> configuration (which was 64k) but so far I don't see a reason why it
> >>> shouldn't fix the issue.
> >>
> >> Awesome. Mind if I put your Tested-by on the patch?
> >>
> > Looks to me like the definition of pmd_huge() on arm64 is broken; pretty
> > sure when I reviewed this original patch I followed the path of both
> > pmd_huge() and pmd_trans_huge() and checked that they don't return true
> > if the entry is clear.  This happens to be the case on both arm and x86,
> > and I probably only looked at the arm code and not the arm64 code.
> > 
> > I'm fine with this patch, but I think we should also merge the
> > following, since by definition, a clear pmd cannot also be a huge pmd:
> > 
> > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > index 2de9d2e..779520b 100644
> > --- a/arch/arm64/mm/hugetlbpage.c
> > +++ b/arch/arm64/mm/hugetlbpage.c
> > @@ -40,7 +40,7 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
> >  
> >  int pmd_huge(pmd_t pmd)
> >  {
> > -	return !(pmd_val(pmd) & PMD_TABLE_BIT);
> > +	return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
> >  }
> >  
> >  int pud_huge(pud_t pud)
> 
> If the convention is for pmd_huge to check for pmd_none, then we don't
> need my patch, and only this should be merged.

Adding Steve on cc. I can see that the mm code checks for pmd_none()
before calling pmd_huge() but I'm not sure it does this all the time
(same goes for pud_huge).

Steve, do you have any more insight here?

-- 
Catalin