Re: [PATCH v8 14/14] KVM: arm64: Use TLBI range-based intructions for unmap

[Shaoqin Huang]

On 8/9/23 07:13, 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 on some systems.
>
> 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 deferred TLB invalidation on the system supporting FWB,
> as the optimization is entirely pointless when the unmap walker
> needs to perform CMOs.
>
> Rename stage2_put_pte() to stage2_unmap_put_pte() as the function
> now serves the stage-2 unmap walker specifically, rather than
> acting generic.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
Reviewed-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
> ---
>   arch/arm64/kvm/hyp/pgtable.c | 40 +++++++++++++++++++++++++++++-------
>   1 file changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 5ef098af17362..eaaae76481fa9 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -831,16 +831,36 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n
>   	smp_store_release(ctx->ptep, new);
>   }
>   
> -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu,
> -			   struct kvm_pgtable_mm_ops *mm_ops)
> +static bool stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt)
>   {
>   	/*
> -	 * Clear the existing PTE, and perform break-before-make with
> -	 * TLB maintenance if it was valid.
> +	 * If FEAT_TLBIRANGE is implemented, defer the individual
> +	 * TLB invalidations until the entire walk is finished, and
> +	 * then use the range-based TLBI instructions to do the
> +	 * invalidations. Condition deferred TLB invalidation on the
> +	 * system supporting FWB as the optimization is entirely
> +	 * pointless when the unmap walker needs to perform CMOs.
> +	 */
> +	return system_supports_tlb_range() && stage2_has_fwb(pgt);
> +}
> +
> +static void stage2_unmap_put_pte(const struct kvm_pgtable_visit_ctx *ctx,
> +				struct kvm_s2_mmu *mmu,
> +				struct kvm_pgtable_mm_ops *mm_ops)
> +{
> +	struct kvm_pgtable *pgt = ctx->arg;
> +
> +	/*
> +	 * Clear the existing PTE, and perform break-before-make if it was
> +	 * valid. Depending on the system support, defer the TLB maintenance
> +	 * for the same until the entire unmap walk is completed.
>   	 */
>   	if (kvm_pte_valid(ctx->old)) {
>   		kvm_clear_pte(ctx->ptep);
> -		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, ctx->addr, ctx->level);
> +
> +		if (!stage2_unmap_defer_tlb_flush(pgt))
> +			kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu,
> +					ctx->addr, ctx->level);
>   	}
>   
>   	mm_ops->put_page(ctx->ptep);
> @@ -1098,7 +1118,7 @@ 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);
> +	stage2_unmap_put_pte(ctx, mmu, mm_ops);
>   
>   	if (need_flush && mm_ops->dcache_clean_inval_poc)
>   		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops),
> @@ -1112,13 +1132,19 @@ 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 kvm_pgtable_walker walker = {
>   		.cb	= stage2_unmap_walker,
>   		.arg	= pgt,
>   		.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 (stage2_unmap_defer_tlb_flush(pgt))
> +		/* Perform the deferred TLB invalidations */
> +		kvm_tlb_flush_vmid_range(pgt->mmu, addr, size);
> +
> +	return ret;
>   }
>   
>   struct stage2_attr_data {

--
Shaoqin