linux-kernel - Re: [PATCH] iommu/vt-d: Fix intel_pasid_max

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Message-ID: <20190430110108.7c751195@jacob-builder>
Date:   Tue, 30 Apr 2019 11:01:08 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, joro@...tes.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        dwmw2@...radead.org, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH] iommu/vt-d: Fix intel_pasid_max_id

On Tue, 30 Apr 2019 09:29:40 +0200
Eric Auger <eric.auger@...hat.com> wrote:

> Extended Capability Register PSS field (PASID Size Supported)
> corresponds to the PASID bit size -1.
> 
> "A value of N in this field indicates hardware supports PASID
> field of N+1 bits (For example, value of 7 in this field,
> indicates 8-bit PASIDs are supported)".
> 
> Fix the computation of intel_pasid_max_id accordingly.
> 
> Fixes: 562831747f62 ("iommu/vt-d: Global PASID name space")
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> ---
>  drivers/iommu/intel-iommu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 28cb713d728c..c3f1bfc81d2e 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -3331,7 +3331,7 @@ static int __init init_dmars(void)
>  		 * than the smallest supported.
>  		 */
>  		if (pasid_supported(iommu)) {
> -			u32 temp = 2 << ecap_pss(iommu->ecap);
> +			u32 temp = 2 << (ecap_pss(iommu->ecap) + 1);
here it is "2 << bits" not "1 << bits", so the original code is correct.

But I agree it would be more clear to the spec. if we do:
1 << (ecap_pss(iommu->ecap) + 1);
>  
>  			intel_pasid_max_id = min_t(u32, temp,
>  						   intel_pasid_max_id);