linux-kernel - Re: [PATCH v2 3/7] iommu/vt-d: Expose ISA direct mapping region via iommu_get_resv

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Date:   Thu, 4 Apr 2019 14:49:05 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     James Sewart <jamessewart@...sta.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        Tom Murphy <tmurphy@...sta.com>,
        Dmitry Safonov <dima@...sta.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/7] iommu/vt-d: Expose ISA direct mapping region via
 iommu_get_resv_regions

Hi James,

I did a sanity test from my end. The test machine fails to boot. I
haven't seen any valuable kernel log. It results in a purple screen.

Best regards,
Lu Baolu

On 3/29/19 11:26 PM, James Sewart wrote:
> Hey Lu,
> 
> I’ve attached a preliminary v3, if you could take a look and run some tests
> that would be great.
> 
> Since v2 i’ve added your default domain type patches, the new device_group
> handler, and incorporated Jacob’s feedback.
> 
>> On 28 Mar 2019, at 18:37, James Sewart <jamessewart@...sta.com> wrote:
>>
>> Hey Lu,
>>
>>> On 26 Mar 2019, at 01:24, Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>>>
>>> Hi James,
>>>
>>> On 3/25/19 8:57 PM, James Sewart wrote:
>>>>>> Theres an issue that if we choose to alloc a new resv_region with type
>>>>>> IOMMU_RESV_DIRECT, we will need to refactor intel_iommu_put_resv_regions
>>>>>> to free this entry type which means refactoring the rmrr regions in
>>>>>> get_resv_regions. Should this work be in this patchset?
>>>>> Do you mean the rmrr regions are not allocated in get_resv_regions, but
>>>>> are freed in put_resv_regions? I think we should fix this in this patch
>>>>> set since this might impact the device passthrough if we don't do it.
>>>> They’re not allocated and not freed currently, only type IOMMU_RESV_MSI is
>>>> freed in put_resv_regions. If we allocate a new resv_region with type
>>>> IOMMU_RESV_DIRECT for the isa region, then it won’t be freed. If we modify
>>>> put_resv_regions to free type IOMMU_RESV_DIRECT, then we will try to free
>>>> the static RMRR regions.
>>>> Either the ISA region is static and not freed as with my implementation,
>>>> or the RMRR regions are converted to be allocated on each call to
>>>> get_resv_regions and freed in put_resv_regions.
>>>
>>> By the way, there's another way in my mind. Let's add a new region type
>>> for LPC devices, e.x. IOMMU_RESV_LPC, and then handle it in the same way
>>> as those MSI regions. Just FYI.
>>
>> This solution would require adding some extra code to
>> iommu_group_create_direct_mappings as currently only type
>> IOMMU_RESV_DIRECT is identity mapped, other types are only reserved.
>>
>>
>>>
>>> Best regards,
>>> Lu Baolu
>>
>> Cheers,
>> James.
> 
> Cheers,
> James.
>