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SubjectRe: [PATCH] powerpc/8xx: Fix clearing of bits 20-23 in ITLB miss
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On Sat, 2020-02-15 at 11:17 +0100, Christophe Leroy wrote:
>
> Le 15/02/2020 à 07:28, Leonardo Bras a écrit :
> > On Sun, 2020-02-09 at 18:14 +0000, Christophe Leroy wrote:
> > > In ITLB miss handled the line supposed to clear bits 20-23 on the
> > > L2 ITLB entry is buggy and does indeed nothing, leading to undefined
> > > value which could allow execution when it shouldn't.
> > >
> > > Properly do the clearing with the relevant instruction.
> > >
> > > Fixes: 74fabcadfd43 ("powerpc/8xx: don't use r12/SPRN_SPRG_SCRATCH2 in TLB Miss handlers")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> > > ---
> > > arch/powerpc/kernel/head_8xx.S | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
> > > index 9922306ae512..073a651787df 100644
> > > --- a/arch/powerpc/kernel/head_8xx.S
> > > +++ b/arch/powerpc/kernel/head_8xx.S
> > > @@ -256,7 +256,7 @@ InstructionTLBMiss:
> > > * set. All other Linux PTE bits control the behavior
> > > * of the MMU.
> > > */
> > > - rlwimi r10, r10, 0, 0x0f00 /* Clear bits 20-23 */
> > > + rlwinm r10, r10, 0, ~0x0f00 /* Clear bits 20-23 */
> > > rlwimi r10, r10, 4, 0x0400 /* Copy _PAGE_EXEC into bit 21 */
> > > ori r10, r10, RPN_PATTERN | 0x200 /* Set 22 and 24-27 */
> > > mtspr SPRN_MI_RPN, r10 /* Update TLB entry */
> >
> > Looks a valid change.
> > rlwimi r10, r10, 0, 0x0f00 means:
> > r10 = ((r10 << 0) & 0x0f00) | (r10 & ~0x0f00) which ends up being
> > r10 = r10
> >
> > On ISA, rlwinm is recommended for clearing high order bits.
> > rlwinm r10, r10, 0, ~0x0f00 means:
> > r10 = (r10 << 0) & ~0x0f00
> >
> > Which does exactly what the comments suggests.
> >
> > FWIW:
> > Reviwed-by: Leonardo Bras <leonardo@linux.ibm.com>
> >
>
> I guess you mean
>
> Reviewed-by: Leonardo Bras <leonardo@linux.ibm.com>

Yes, sorry for the typo.
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