Michael Ellerman <m...@ellerman.id.au> writes: > From: Oliver O'Halloran <ooh...@gmail.com> > > The Radix MMU translation tree as defined in ISA v3.0 contains two > different types of entry, directories and leaves. Leaves are > identified by _PAGE_PTE being set. > > The formats of the two entries are different, with the directory > entries containing no spare bits for use by software. In particular > the bit we use for _PAGE_DEVMAP is not reserved for software, and is > part of the NLB (Next Level Base) field, essentially the address of > the next level in the tree. > > Note that the Linux pte_t is not == _PAGE_PTE. A huge page pmd > entry (or devmap!) is also a leaf and so has _PAGE_PTE set, even > though we use a pmd_t for it in Linux. > > The fix is to ensure that the pmd/pte_devmap() confirm they are > looking at a leaf entry (_PAGE_PTE) as well as checking _PAGE_DEVMAP. >
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> > Signed-off-by: Oliver O'Halloran <ooh...@gmail.com> > Tested-by: Laurent Vivier <lviv...@redhat.com> > Tested-by: Jose Ricardo Ziviani <jos...@linux.vnet.ibm.com> > Reviewed-by: Suraj Jitindar Singh <sjitindarsi...@gmail.com> > [mpe: Add a comment in the code and flesh out change log] > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > v2: Add a comment in the code and flesh out change log > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index d1da415e283c..818a58fc3f4f 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -608,9 +608,17 @@ static inline pte_t pte_mkdevmap(pte_t pte) > return __pte(pte_val(pte) | _PAGE_SPECIAL|_PAGE_DEVMAP); > } > > +/* > + * This is potentially called with a pmd as the argument, in which case it's > not > + * safe to check _PAGE_DEVMAP unless we also confirm that _PAGE_PTE is set. > + * That's because the bit we use for _PAGE_DEVMAP is not reserved for > software > + * use in page directory entries (ie. non-ptes). > + */ > static inline int pte_devmap(pte_t pte) > { > - return !!(pte_raw(pte) & cpu_to_be64(_PAGE_DEVMAP)); > + u64 mask = cpu_to_be64(_PAGE_DEVMAP | _PAGE_PTE); > + > + return (pte_raw(pte) & mask) == mask; > } > > static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) > -- > 2.7.4