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

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Message-ID: <BN9PR11MB527613D6C657A4AE0DE169758C27A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 27 Jun 2023 08:15:09 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Liu, Jingqi" <jingqi.liu@...el.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 1/2] iommu: Prevent RESV_DIRECT devices from blocking
 domains

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 27, 2023 4:01 PM
> 
> On 2023/6/27 15:54, Tian, Kevin wrote:
> >> From: Baolu Lu <baolu.lu@...ux.intel.com>
> >> Sent: Tuesday, June 13, 2023 11:15 AM
> >>
> >> On 6/12/23 4:28 PM, Liu, Jingqi wrote:
> >>> On 6/7/2023 11:51 AM, Lu Baolu wrote:
> >>>> -
> >>>> -    BUG_ON(!domain->pgsize_bitmap);
> >>>> -
> >>>> -    pg_size = 1UL << __ffs(domain->pgsize_bitmap);
> >>>> +    pg_size = domain->pgsize_bitmap ? 1UL <<
> >>>> __ffs(domain->pgsize_bitmap) : 0;
> >>> Would it be better to add the following check here?
> >>>       if (WARN_ON(!pg_size))
> >>>               return -EINVAL;
> >>>
> >>> Instead of checking latter in the loop as follows.
> >>>       if (WARN_ON_ONCE(!pg_size)) {
> >>>               ret = -EINVAL;
> >>>               goto out;
> >>>       }
> >>
> >> I am afraid no. Only the paging domains need a valid pg_size. That's the
> >> reason why I put it after the iommu_is_dma_domain() check. The
> previous
> >> code has the same behavior too.
> >>
> >
> > You could also add the dma domain check here. pg_size is static
> > then it makes more sense to verify it once instead of in a loop.
> 
> Agreed. Does below additional change make sense?
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index e59de7852067..3be88b5f36bb 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -962,6 +962,9 @@ static int
> iommu_create_device_direct_mappings(struct iommu_domain *domain,
>          pg_size = domain->pgsize_bitmap ? 1UL <<
> __ffs(domain->pgsize_bitmap) : 0;
>          INIT_LIST_HEAD(&mappings);
> 
> +       if (WARN_ON_ONCE((domain->type & __IOMMU_DOMAIN_PAGING)
> &&
> !pg_size))
> +               return -EINVAL;

what's the reason of not using iommu_is_dma_domain()? this is called
in the probe path only for the default domain. Otherwise if you change
like this then you also want to change the check in the loop later to be
consistent.

> +
>          iommu_get_resv_regions(dev, &mappings);
> 
>          /* We need to consider overlapping regions for different devices */
> @@ -977,11 +980,6 @@ static int
> iommu_create_device_direct_mappings(struct iommu_domain *domain,
>                      !iommu_is_dma_domain(domain))
>                          continue;
> 
> -               if (WARN_ON_ONCE(!pg_size)) {
> -                       ret = -EINVAL;
> -                       goto out;
> -               }
> -
>                  start = ALIGN(entry->start, pg_size);
>                  end   = ALIGN(entry->start + entry->length, pg_size);
> 
> Best regards,
> baolu