Re: [edk2-devel] [PATCH edk2-stable202305] ArmPkg/ArmMmuLib: Add missing ISB after page table update

["Ard Biesheuvel" <ardb@kernel.org>]

PR here: https://github.com/tianocore/edk2/pull/4418

I cannot set the 'push' label myself, it seems.



On Mon, 22 May 2023 at 16:10, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
>
> Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
>
> No objection to merging for the stable tag.
>
> Mike
>
> > -----Original Message-----
> > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Leif
> > Lindholm
> > Sent: Monday, May 22, 2023 3:56 AM
> > To: Ard Biesheuvel <ardb@kernel.org>
> > Cc: devel@edk2.groups.io; Gao, Liming <gaoliming@byosoft.com.cn>;
> > Kinney, Michael D <michael.d.kinney@intel.com>; Oliver Steffen
> > <osteffen@redhat.com>
> > Subject: Re: [edk2-devel] [PATCH edk2-stable202305] ArmPkg/ArmMmuLib:
> > Add missing ISB after page table update
> >
> > On Sat, May 20, 2023 at 11:19:58 +0200, Ard Biesheuvel wrote:
> > > The helper that updates live page table entries writes a zero entry,
> > > invalidates the covered address range from the TLBs, and finally writes
> > > the actual entry. This ensures that no TLB conflicts can occur.
> > >
> > > Writing the final entry needs to complete before any translations can be
> > > performed, as otherwise, the zero entry, which describes an invalid
> > > translation, may be observed by the page table walker, resulting in a
> > > translation fault. For this reason, the final write is followed by a DSB
> > > barrier instruction.
> > >
> > > However, this barrier will not stall the pipeline, and instruction
> > > fetches may still hit this invalid translation, as has been observed and
> > > reported by Oliver. To ensure that the new translation is fully active
> > > before returning from this helper, we have to insert an ISB barrier as
> > > well.
> > >
> > > Cc: Liming Gao <gaoliming@byosoft.com.cn>
> > > Cc: Leif Lindholm <quic_llindhol@quicinc.com>
> > > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > > Reported-by: Oliver Steffen <osteffen@redhat.com>
> > > Tested-by: Oliver Steffen <osteffen@redhat.com>
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >
> > Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
> >
> > We need this in the stable tag.
> >
> > Note: the isb instruction forces the synchronization of certain
> > architectural events. It has no other effects. I.e., any issues
> > exposed by this addition would already have been present before it.
> >
> > As such, I would suggest this addition need *not* affect the stable
> > tag schedule.
> >
> > /
> >     Leif
> >
> > > ---
> > >  ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git
> > a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
> > b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
> > > index 887439bc042f0f16..1f0d8057926933d7 100644
> > > --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
> > > +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
> > > @@ -65,6 +65,7 @@
> > >    // write updated entry
> > >    str   x1, [x0]
> > >    dsb   nshst
> > > +  isb
> > >
> > >  .L2_\@:
> > >    .endm
> > > --
> > > 2.39.2
> > >
> >
> >
> > 
> >
>