linux-kernel - Re: [PATCH 1/2] iommu/vt-d: Avoid unnecessary global IRTE cache invalidation

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Date:   Mon, 19 Sep 2022 01:29:19 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iommu/vt-d: Avoid unnecessary global IRTE cache
 invalidation

On Mon, Sep 19, 2022 at 02:25:22PM +0800, Lu Baolu wrote:
> Some VT-d hardware implementations invalidate all interrupt remapping
> hardware translation caches as part of SIRTP flow. The VT-d spec adds
> a ESIRTPS (Enhanced Set Interrupt Remap 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: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

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

> ---
>  drivers/iommu/intel/iommu.h         | 1 +
>  drivers/iommu/intel/irq_remapping.c | 3 ++-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index eef1a166b855..5407d82df4d1 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -146,6 +146,7 @@
>  /*
>   * Decoding Capability Register
>   */
> +#define cap_esirtps(c)		(((c) >> 62) & 1)
>  #define cap_fl5lp_support(c)	(((c) >> 60) & 1)
>  #define cap_pi_support(c)	(((c) >> 59) & 1)
>  #define cap_fl1gp_support(c)	(((c) >> 56) & 1)
> diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
> index 2e9683e970f8..b4a91fbd1c2f 100644
> --- a/drivers/iommu/intel/irq_remapping.c
> +++ b/drivers/iommu/intel/irq_remapping.c
> @@ -494,7 +494,8 @@ static void iommu_set_irq_remapping(struct intel_iommu *iommu, int mode)
>  	 * Global invalidation of interrupt entry cache to make sure the
>  	 * hardware uses the new irq remapping table.
>  	 */
> -	qi_global_iec(iommu);
> +	if (!cap_esirtps(iommu->cap))
> +		qi_global_iec(iommu);
>  }
>  
>  static void iommu_enable_irq_remapping(struct intel_iommu *iommu)
> -- 
> 2.34.1
>