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

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Date:   Tue, 27 Jun 2023 16:01:01 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.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:     baolu.lu@...ux.intel.com,
        "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

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;
+
         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