Re: [PATCH v2 18/24] iommu: Express DMA strictness via the domain type

[Lu Baolu]

On 2021/7/29 17:36, Robin Murphy wrote:
> On 2021-07-29 08:13, Lu Baolu wrote:
> > Hi Robin,
> >
> > On 7/28/21 11:58 PM, Robin Murphy wrote:
> > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > > index 982545234cf3..eecb5657de69 100644
> > > --- a/drivers/iommu/iommu.c
> > > +++ b/drivers/iommu/iommu.c
> > > @@ -136,6 +136,9 @@ static int __init iommu_subsys_init(void)
> > >           }
> > >       }
> > > +    if (!iommu_default_passthrough() && !iommu_dma_strict)
> > > +        iommu_def_domain_type = IOMMU_DOMAIN_DMA_FQ;
> >
> > iommu_dma_strict could be changed later by the vendor iommu driver via
> > iommu_set_dma_strict(). This seems not to be the right place to set
> > iommu_def_domain_type.
>
> Ah yes, good catch once again, thanks!
>
> I think this *is* the right place to initially set it to honour the 
> command-line option, since that matches what we do for passthrough. 
> However also like passthrough we'll need to keep things in sync if it's 
> updated later, like this:
>
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 87d7b299436e..593d4555bc57 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -359,6 +359,8 @@ early_param("iommu.strict", iommu_dma_setup);
>   void iommu_set_dma_strict(void)
>   {
>          iommu_dma_strict = true;
> +       if (iommu_def_domain_type == IOMMU_DOMAIN_DMA_FQ)
> +               iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>   }
>
>   static ssize_t iommu_group_attr_show(struct kobject *kobj,
>
>
> Does that seem reasonable? I'm not sure there's any cleaner way to do it 
> since we don't want to inadvertently clobber the default type if the 
> user has given us something funky like "intel_iommu=strict 
> iommu.passthrough=1".

Yeah! It's reasonable as far as I can see.

Best regards,
baolu

> Cheers,
> Robin.
>
> > > +
> > >       pr_info("Default domain type: %s %s\n",
> > >           iommu_domain_type_str(iommu_def_domain_type),
> > >           (iommu_cmd_line & IOMMU_CMD_LINE_DMA_API) ?
> >
> > Best regards,
> > baolu