Re: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking domains

[Baolu Lu]

On 2023/7/21 11:07, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > 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"?

How about

 * @require_direct: device requires IOMMU_RESV_DIRECT reserved regions

?

> > @@ -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?

Jason answered this.

> > @@ -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/

Updated. Thanks!

Best regards,
baolu