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SubjectRe: [PATCH 2/2] iommu/vt-d: Avoid unnecessary global DMA cache invalidation
On Mon, Sep 19, 2022 at 02:25:23PM +0800, Lu Baolu wrote:
> Some VT-d hardware implementations invalidate all DMA remapping hardware
> translation caches as part of SRTP flow. The VT-d spec adds a ESRTPS
> (Enhanced Set Root Table Pointer Support, section 11.4.2 in VT-d spec)
> capability bit to indicate this. With this bit set, software has no need
> to issue the global invalidation request.
>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com

> ---
> drivers/iommu/intel/iommu.h | 1 +
> drivers/iommu/intel/iommu.c | 7 +++++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index 5407d82df4d1..251a609fdce3 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -146,6 +146,7 @@
> /*
> * Decoding Capability Register
> */
> +#define cap_esrtps(c) (((c) >> 63) & 1)
> #define cap_esirtps(c) (((c) >> 62) & 1)
> #define cap_fl5lp_support(c) (((c) >> 60) & 1)
> #define cap_pi_support(c) (((c) >> 59) & 1)
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 8e5d99197d39..c20f3e060bac 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1239,6 +1239,13 @@ static void iommu_set_root_entry(struct intel_iommu *iommu)
>
> raw_spin_unlock_irqrestore(&iommu->register_lock, flag);
>
> + /*
> + * Hardware invalidates all DMA remapping hardware translation
> + * caches as part of SRTP flow.
> + */
> + if (cap_esrtps(iommu->cap))
> + return;
> +
> iommu->flush.flush_context(iommu, 0, 0, 0, DMA_CCMD_GLOBAL_INVL);
> if (sm_supported(iommu))
> qi_flush_pasid_cache(iommu, 0, QI_PC_GLOBAL, 0);
> --
> 2.34.1
>

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