On Fri, May 12, 2023 at 10:02 AM Oliver Upton <oliver.upton@xxxxxxxxx> wrote:
>
> Hi Raghavendra,
>
> On Fri, Apr 14, 2023 at 05:29:22PM +0000, Raghavendra Rao Ananta wrote:
> > The current implementation of the stage-2 unmap walker traverses
> > the given range and, as a part of break-before-make, performs
> > TLB invalidations with a DSB for every PTE. A multitude of this
> > combination could cause a performance bottleneck.
> >
> > Hence, if the system supports FEAT_TLBIRANGE, defer the TLB
> > invalidations until the entire walk is finished, and then
> > use range-based instructions to invalidate the TLBs in one go.
> > Condition this upon S2FWB in order to avoid walking the page-table
> > again to perform the CMOs after issuing the TLBI.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> > Suggested-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> > ---
> > arch/arm64/kvm/hyp/pgtable.c | 33 +++++++++++++++++++++++++++++----
> > 1 file changed, 29 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> > index 3f136e35feb5e..bcb748e3566c7 100644
> > --- a/arch/arm64/kvm/hyp/pgtable.c
> > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > @@ -987,10 +987,16 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > return ret;
> > }
> >
> > +struct stage2_unmap_data {
> > + struct kvm_pgtable *pgt;
> > + bool skip_pte_tlbis;
> > +};
> > +
> > static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
> > enum kvm_pgtable_walk_flags visit)
> > {
> > - struct kvm_pgtable *pgt = ctx->arg;
> > + struct stage2_unmap_data *unmap_data = ctx->arg;
> > + struct kvm_pgtable *pgt = unmap_data->pgt;
> > struct kvm_s2_mmu *mmu = pgt->mmu;
> > struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> > kvm_pte_t *childp = NULL;
> > @@ -1018,7 +1024,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
> > * block entry and rely on the remaining portions being faulted
> > * back lazily.
> > */
> > - stage2_put_pte(ctx, mmu, mm_ops, false);
> > + stage2_put_pte(ctx, mmu, mm_ops, unmap_data->skip_pte_tlbis);
> >
> > if (need_flush && mm_ops->dcache_clean_inval_poc)
> > mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops),
> > @@ -1032,13 +1038,32 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
> >
> > int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
> > {
> > + int ret;
> > + struct stage2_unmap_data unmap_data = {
> > + .pgt = pgt,
> > + /*
> > + * If FEAT_TLBIRANGE is implemented, defer the individial PTE
> > + * TLB invalidations until the entire walk is finished, and
> > + * then use the range-based TLBI instructions to do the
> > + * invalidations. Condition this upon S2FWB in order to avoid
> > + * a page-table walk again to perform the CMOs after TLBI.
> > + */
> > + .skip_pte_tlbis = system_supports_tlb_range() &&
> > + stage2_has_fwb(pgt),
>
> Why can't the underlying walker just call these two helpers directly?
> There are static keys behind these...
>
I wasn't aware of that. Although, I tried to look into the
definitions, but couldn't understand how static keys are at play here.
By any chance are you referring to the alternative_has_feature_*()
implementations when checking for cpu capabilities?
Thank you.
Raghavendra
> > + };
> > struct kvm_pgtable_walker walker = {
> > .cb = stage2_unmap_walker,
> > - .arg = pgt,
> > + .arg = &unmap_data,
> > .flags = KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
> > };
> >
> > - return kvm_pgtable_walk(pgt, addr, size, &walker);
> > + ret = kvm_pgtable_walk(pgt, addr, size, &walker);
> > + if (unmap_data.skip_pte_tlbis)
> > + /* Perform the deferred TLB invalidations */
> > + kvm_call_hyp(__kvm_tlb_flush_vmid_range, pgt->mmu,
> > + addr, addr + size);
> > +
> > + return ret;
> > }
> >
> > struct stage2_attr_data {
> > --
> > 2.40.0.634.g4ca3ef3211-goog
> >
>
> --
> Thanks,
> Oliver
