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

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Date:   Tue, 26 Mar 2019 09:24:20 +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,

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.

Best regards,
Lu Baolu