On Thu, 13 Apr 2023 01:09:20 +0100,
Oliver Upton <oliver.upton@xxxxxxxxx> wrote:
>
> Hi Marc,
>
> On Sat, Apr 08, 2023 at 05:04:24PM +0100, Marc Zyngier wrote:
> > A TLBI from EL2 impacting EL1 involves messing with the EL1&0
> > translation regime, and the page table walker may still be
> > performing speculative walks.
> >
> > Piggyback on the existing DSBs to always have a DSB ISH that
> > will synchronise all load/store operations that the PTW may
> > still have.
> >
> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > ---
> > arch/arm64/kvm/hyp/nvhe/tlb.c | 24 +++++++++++++++++++-----
> > 1 file changed, 19 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
> > index d296d617f589..e86dd04d49ff 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/tlb.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/tlb.c
> > @@ -17,6 +17,23 @@ struct tlb_inv_context {
> > static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
> > struct tlb_inv_context *cxt)
> > {
> > + /*
> > + * We have two requirements:
> > + *
> > + * - ensure that the page table updates are visible to all
> > + * CPUs, for which a dsb(ishst) is what we need
> > + *
> > + * - complete any speculative page table walk started before
> > + * we trapped to EL2 so that we can mess with the MM
> > + * registers out of context, for which dsb(nsh) is enough
> > + *
> > + * The composition of these two barriers is a dsb(ish). This
> > + * might be slightly over the top for non-shareable TLBIs, but
> > + * they are so vanishingly rare that it isn't worth the
> > + * complexity.
> > + */
> > + dsb(ish);
> > +
>
> Ricardo is carrying a patch for non-shareable TLBIs on permission
> relaxation [*], and he's found that it produces some rather desirable
> performance improvements. I appreciate the elegance of your approach,
> but given what's coming does it make sense to have the TLBI handlers
> continue to explicitly perform the appropriate DSB?
Ah, I forgot about my own patch! :D
Right, let me see if I can do something clever here...
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
