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SubjectRe: [PATCH 0/5] iommu/vt-d: Consolidate various cache flush ops
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Hi David,

On 12/3/19 4:49 PM, David Woodhouse wrote:
> On Fri, 2019-11-22 at 11:04 +0800, Lu Baolu wrote:
>> Intel VT-d 3.0 introduces more caches and interfaces for software to
>> flush when it runs in the scalable mode. Currently various cache flush
>> helpers are scattered around. This consolidates them by putting them in
>> the existing iommu_flush structure.
>>
>> /* struct iommu_flush - Intel IOMMU cache invalidation ops
>> *
>> * @cc_inv: invalidate context cache
>> * @iotlb_inv: Invalidate IOTLB and paging structure caches when software
>> * has changed second-level tables.
>> * @p_iotlb_inv: Invalidate IOTLB and paging structure caches when software
>> * has changed first-level tables.
>> * @pc_inv: invalidate pasid cache
>> * @dev_tlb_inv: invalidate cached mappings used by requests-without-PASID
>> * from the Device-TLB on a endpoint device.
>> * @p_dev_tlb_inv: invalidate cached mappings used by requests-with-PASID
>> * from the Device-TLB on an endpoint device
>> */
>> struct iommu_flush {
>> void (*cc_inv)(struct intel_iommu *iommu, u16 did,
>> u16 sid, u8 fm, u64 type);
>> void (*iotlb_inv)(struct intel_iommu *iommu, u16 did, u64 addr,
>> unsigned int size_order, u64 type);
>> void (*p_iotlb_inv)(struct intel_iommu *iommu, u16 did, u32 pasid,
>> u64 addr, unsigned long npages, bool ih);
>> void (*pc_inv)(struct intel_iommu *iommu, u16 did, u32 pasid,
>> u64 granu);
>> void (*dev_tlb_inv)(struct intel_iommu *iommu, u16 sid, u16 pfsid,
>> u16 qdep, u64 addr, unsigned int mask);
>> void (*p_dev_tlb_inv)(struct intel_iommu *iommu, u16 sid, u16 pfsid,
>> u32 pasid, u16 qdep, u64 addr,
>> unsigned long npages);
>> };
>>
>> The name of each cache flush ops is defined according to the spec section 6.5
>> so that people are easy to look up them in the spec.
>
> Hm, indirect function calls are quite expensive these days.

Good consideration. Thanks!

>
> I would have preferred to go in the opposite direction, since surely
> aren't going to have *many* of these implementations. Currently there's
> only one for register-based and one for queued invalidation, right?
> Even if VT-d 3.0 throws an extra version in, I think I'd prefer to take
> out the indirection completely and have an if/then helper.
>
> Would love to see a microbenchmark of unmap operations before and after
> this patch series with retpoline enabled, to see the effect.

Yes. Need some micro-bench tests to address the concern.

Best regards,
baolu

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