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

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Date:   Tue, 30 Apr 2019 22:37:53 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     eric.auger.pro@...il.com, joro@...tes.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        dwmw2@...radead.org
Subject: Re: [PATCH] iommu/vt-d: Fix intel_pasid_max_id

Hi Jacob,

On 4/30/19 8:01 PM, Jacob Pan wrote:
> 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);
Oups OK, my eyes. Forget it :-(

Thanks

Eric
>>  
>>  			intel_pasid_max_id = min_t(u32, temp,
>>  						   intel_pasid_max_id);
>