linux-kernel - Re: [PATCH 3/3] iommu/arm-smmu-v3: Add a max_tlbi_ops for __arm_smmu_tlb_inv

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Date:   Tue, 22 Aug 2023 16:04:10 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     <will@...nel.org>, <jgg@...dia.com>, <joro@...tes.org>,
        <jean-philippe@...aro.org>, <apopple@...dia.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>
Subject: Re: [PATCH 3/3] iommu/arm-smmu-v3: Add a max_tlbi_ops for
 __arm_smmu_tlb_inv_range()

Hi Robin,

On Tue, Aug 22, 2023 at 09:32:26AM -0700, Nicolin Chen wrote:
> On Tue, Aug 22, 2023 at 10:30:35AM +0100, Robin Murphy wrote:
> 
> > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > index d6c647e1eb01..3f0db30932bd 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > @@ -1897,7 +1897,14 @@ static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd,
> > >       if (!size)
> > >               return;
> > > 
> > > -     if (smmu->features & ARM_SMMU_FEAT_RANGE_INV) {
> > > +     if (!(smmu->features & ARM_SMMU_FEAT_RANGE_INV)) {
> > > +             /*
> > > +              * When the size reaches a threshold, replace per-granule TLBI
> > > +              * commands with one single per-asid or per-vmid TLBI command.
> > > +              */
> > > +             if (size >= granule * smmu_domain->max_tlbi_ops)
> > > +                     return arm_smmu_tlb_inv_domain(smmu_domain);
> > 
> > This looks like it's at the wrong level - we should have figured this
> > out before we got as far as low-level command-building. I'd have thought
> > it would be a case of short-circuiting directly from
> > arm_smmu_tlb_inv_range_domain() to arm_smmu_tlb_inv_context().
> 
> OK, I could do that. We would have copies of this same routine
> though. Also, the shortcut applies to !ARM_SMMU_FEAT_RANGE_INV
> cases only, so this function feels convenient to me.

I was trying to say that we would need the same piece in both
arm_smmu_tlb_inv_range_domain() and arm_smmu_tlb_inv_range_asid(),
though the latter one only needs to call arm_smmu_tlb_inv_asid().

Also, arm_smmu_tlb_inv_context() does a full range ATC invalidation
instead of a given range like what arm_smmu_tlb_inv_range_domain()
currently does. So, it might be a bit overkill.

Combining all your comments, we'd have something like this:

-------------------------------------------------------------------
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 7614739ea2c1..2967a6634c7c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1937,12 +1937,22 @@ static void arm_smmu_tlb_inv_range_domain(unsigned long iova, size_t size,
 					  size_t granule, bool leaf,
 					  struct arm_smmu_domain *smmu_domain)
 {
+	struct io_pgtable_cfg *cfg =
+		&io_pgtable_ops_to_pgtable(smmu_domain->pgtbl_ops)->cfg;
 	struct arm_smmu_cmdq_ent cmd = {
 		.tlbi = {
 			.leaf	= leaf,
 		},
 	};
 
+	/*
+	 * If the given size is too large that would end up with too many TLBI
+	 * commands in CMDQ, short circuit directly to a full invalidation
+	 */
+	if (!(smmu_domain->smmu->features & ARM_SMMU_FEAT_RANGE_INV) &&
+	    size >= granule * (1UL << cfg->bits_per_level))
+		return arm_smmu_tlb_inv_context(smmu_domain);
+
 	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
 		cmd.opcode	= smmu_domain->smmu->features & ARM_SMMU_FEAT_E2H ?
 				  CMDQ_OP_TLBI_EL2_VA : CMDQ_OP_TLBI_NH_VA;
@@ -1964,6 +1974,8 @@ void arm_smmu_tlb_inv_range_asid(unsigned long iova, size_t size, int asid,
 				 size_t granule, bool leaf,
 				 struct arm_smmu_domain *smmu_domain)
 {
+	struct io_pgtable_cfg *cfg =
+		&io_pgtable_ops_to_pgtable(smmu_domain->pgtbl_ops)->cfg;
 	struct arm_smmu_cmdq_ent cmd = {
 		.opcode	= smmu_domain->smmu->features & ARM_SMMU_FEAT_E2H ?
 			  CMDQ_OP_TLBI_EL2_VA : CMDQ_OP_TLBI_NH_VA,
@@ -1973,6 +1985,14 @@ void arm_smmu_tlb_inv_range_asid(unsigned long iova, size_t size, int asid,
 		},
 	};
 
+	/*
+	 * If the given size is too large that would end up with too many TLBI
+	 * commands in CMDQ, short circuit directly to a full invalidation
+	 */
+	if (!(smmu_domain->smmu->features & ARM_SMMU_FEAT_RANGE_INV) &&
+	    size >= granule * (1UL << cfg->bits_per_level))
+		return arm_smmu_tlb_inv_asid(smmu_domain->smmu, asid);
+
 	__arm_smmu_tlb_inv_range(&cmd, iova, size, granule, smmu_domain);
 }
 
-------------------------------------------------------------------

You're sure that you prefer this, right?

Thanks
Nicolin