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

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Message-ID: <1c8f6bf4-f0ad-2888-ada0-056c12647c41@linux.intel.com>
Date:   Tue, 27 Jun 2023 16:21:56 +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 16:15, Tian, Kevin wrote:
>> 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.
> 

Yes. iommu_is_dma_domain() is better.

Best regards,
baolu