linux-kernel - Re: [PATCH v1 3/4] iommu/arm-smmu-v3: Decouple vmid from S2 nest

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Message-ID: <20250305170157.GB133783@nvidia.com>
Date: Wed, 5 Mar 2025 13:01:57 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH v1 3/4] iommu/arm-smmu-v3: Decouple vmid from S2
 nest_parent domain

On Tue, Mar 04, 2025 at 09:04:02PM -0800, Nicolin Chen wrote:
> @@ -2249,10 +2249,22 @@ static void arm_smmu_tlb_inv_context(void *cookie)
>  	 */
>  	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
>  		arm_smmu_tlb_inv_asid(smmu, smmu_domain->cd.asid);
> -	} else {
> +	} else if (!smmu_domain->nest_parent) {
>  		cmd.opcode	= CMDQ_OP_TLBI_S12_VMALL;
>  		cmd.tlbi.vmid	= smmu_domain->s2_cfg.vmid;
>  		arm_smmu_cmdq_issue_cmd_with_sync(smmu, &cmd);
> +	} else {
> +		struct arm_vsmmu *vsmmu, *next;
> +		unsigned long flags;
> +
> +		cmd.opcode = CMDQ_OP_TLBI_S12_VMALL;
> +		spin_lock_irqsave(&smmu_domain->vsmmus.lock, flags);
> +		list_for_each_entry_safe(vsmmu, next, &smmu_domain->vsmmus.list,
> +					 vsmmus_elm) {
> +			cmd.tlbi.vmid = vsmmu->vmid;
> +			arm_smmu_cmdq_issue_cmd_with_sync(smmu, &cmd);
> +		}
> +		spin_unlock_irqrestore(&smmu_domain->vsmmus.lock, flags);
>  	}

I see.. So this just makes a 3rd classification of invalidation
protocol that uses a spinlock and linked list

>  	arm_smmu_atc_inv_domain(smmu_domain, 0, 0);

This is no good, arm_smmu_atc_inv_domain() is invalidating against the
instance that created the domain.

IMHO if you do this you should set domain->iommu = NULL to indicate
that the iommu is non-valid in this mode to catch issues.

Jason