linux-kernel - RE: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking domains

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Date:   Fri, 21 Jul 2023 03:07:47 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Nicolin Chen <nicolinc@...dia.com>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: RE: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking
 domains

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, July 13, 2023 12:33 PM
> 
> @@ -409,6 +409,7 @@ struct iommu_fault_param {
>   * @priv:	 IOMMU Driver private data
>   * @max_pasids:  number of PASIDs this device can consume
>   * @attach_deferred: the dma domain attachment is deferred
> + * @requires_direct: The driver requested IOMMU_RESV_DIRECT

it's not accurate to say "driver requested" as it's a device attribute.

s/requires_direct/require_direct/

what about "has_resv_direct"?

> @@ -959,14 +959,12 @@ static int
> iommu_create_device_direct_mappings(struct iommu_domain *domain,
>  	unsigned long pg_size;
>  	int ret = 0;
> 
> -	if (!iommu_is_dma_domain(domain))
> -		return 0;
> -
> -	BUG_ON(!domain->pgsize_bitmap);
> -
> -	pg_size = 1UL << __ffs(domain->pgsize_bitmap);
> +	pg_size = domain->pgsize_bitmap ? 1UL << __ffs(domain-
> >pgsize_bitmap) : 0;
>  	INIT_LIST_HEAD(&mappings);
> 
> +	if (WARN_ON_ONCE(iommu_is_dma_domain(domain) && !pg_size))
> +		return -EINVAL;
> +
>  	iommu_get_resv_regions(dev, &mappings);
> 
>  	/* We need to consider overlapping regions for different devices */
> @@ -974,13 +972,17 @@ static int
> iommu_create_device_direct_mappings(struct iommu_domain *domain,
>  		dma_addr_t start, end, addr;
>  		size_t map_size = 0;
> 
> +		if (entry->type == IOMMU_RESV_DIRECT)
> +			dev->iommu->requires_direct = 1;
> +
> +		if ((entry->type != IOMMU_RESV_DIRECT &&
> +		     entry->type != IOMMU_RESV_DIRECT_RELAXABLE) ||
> +		    !iommu_is_dma_domain(domain))
> +			continue;
> +
>  		start = ALIGN(entry->start, pg_size);
>  		end   = ALIGN(entry->start + entry->length, pg_size);
> 
> -		if (entry->type != IOMMU_RESV_DIRECT &&
> -		    entry->type != IOMMU_RESV_DIRECT_RELAXABLE)
> -			continue;
> -
>  		for (addr = start; addr <= end; addr += pg_size) {
>  			phys_addr_t phys_addr;
> 

piggybacking a device attribute detection in a function which tries to
populate domain mappings is a bit confusing.

Does it work better to introduce a new function to detect this attribute
and has it directly called in the probe path? 

> @@ -2121,6 +2123,21 @@ static int __iommu_device_set_domain(struct
> iommu_group *group,
>  {
>  	int ret;
> 
> +	/*
> +	 * If the driver has requested IOMMU_RESV_DIRECT then we cannot

ditto. It's not requested by the driver.

> allow
> +	 * the blocking domain to be attached as it does not contain the
> +	 * required 1:1 mapping. This test effectively exclusive the device

s/exclusive/excludes/