linux-kernel - Re: [PATCH v3 7/7] iommu/riscv: Paging domain support

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Date: Thu, 2 May 2024 11:50:35 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Tomasz Jeznach <tjeznach@...osinc.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Paul Walmsley <paul.walmsley@...ive.com>
Cc: baolu.lu@...ux.intel.com, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Anup Patel <apatel@...tanamicro.com>,
 Sunil V L <sunilvl@...tanamicro.com>, Nick Kossifidis <mick@....forth.gr>,
 Sebastien Boeuf <seb@...osinc.com>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, devicetree@...r.kernel.org, iommu@...ts.linux.dev,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux@...osinc.com
Subject: Re: [PATCH v3 7/7] iommu/riscv: Paging domain support

On 5/1/24 4:01 AM, Tomasz Jeznach wrote:
> +/*
> + * Send IOTLB.INVAL for whole address space for ranges larger than 2MB.
> + * This limit will be replaced with range invalidations, if supported by
> + * the hardware, when RISC-V IOMMU architecture specification update for
> + * range invalidations update will be available.
> + */
> +#define RISCV_IOMMU_IOTLB_INVAL_LIMIT	(2 << 20)
> +
> +static void riscv_iommu_iotlb_inval(struct riscv_iommu_domain *domain,
> +				    unsigned long start, unsigned long end)
> +{
> +	struct riscv_iommu_bond *bond;
> +	struct riscv_iommu_device *iommu, *prev;
> +	struct riscv_iommu_command cmd;
> +	unsigned long len = end - start + 1;
> +	unsigned long iova;
> +
> +	rcu_read_lock();
> +
> +	prev = NULL;
> +	list_for_each_entry_rcu(bond, &domain->bonds, list) {
> +		iommu = dev_to_iommu(bond->dev);
> +
> +		riscv_iommu_cmd_inval_vma(&cmd);
> +		riscv_iommu_cmd_inval_set_pscid(&cmd, domain->pscid);
> +		if (len && len >= RISCV_IOMMU_IOTLB_INVAL_LIMIT) {
> +			for (iova = start; iova < end; iova += PAGE_SIZE) {
> +				riscv_iommu_cmd_inval_set_addr(&cmd, iova);
> +				riscv_iommu_cmd_send(iommu, &cmd, 0);
> +			}
> +		} else {
> +			riscv_iommu_cmd_send(iommu, &cmd, 0);
> +		}
> +
> +		/*
> +		 * IOTLB invalidation request can be safely omitted if already sent
> +		 * to the IOMMU for the same PSCID, and with domain->bonds list
> +		 * arranged based on the device's IOMMU, it's sufficient to check
> +		 * last device the invalidation was sent to.
> +		 */
> +		if (iommu == prev)
> +			continue;
> +
> +		prev = iommu;
> +		riscv_iommu_cmd_send(iommu, &cmd, 0);
> +	}

I don't quite follow why not moving "if (iommu == prev)" check to the
top and removing the last riscv_iommu_cmd_send(). My understanding is
that we could make it simply like below:

	prev = NULL;
	list_for_each_entry_rcu(bond, &domain->bonds, list) {
		iommu = dev_to_iommu(bond->dev);
		if (iommu == prev)
			continue;

		/*
		 * Send an invalidation request to the request queue
		 * without wait.
		 */
		... ...

		prev = iommu;
	}

> +
> +	prev = NULL;
> +	list_for_each_entry_rcu(bond, &domain->bonds, list) {
> +		iommu = dev_to_iommu(bond->dev);
> +		if (iommu == prev)
> +			continue;
> +
> +		prev = iommu;
> +		riscv_iommu_cmd_iofence(&cmd);
> +		riscv_iommu_cmd_send(iommu, &cmd, RISCV_IOMMU_QUEUE_TIMEOUT);
> +	}
> +	rcu_read_unlock();
> +}

Best regards,
baolu