linux-kernel - Re: [PATCH 4/5] iommu/vt-d: Remove domain_update_iommu

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Message-ID: <d42cba21-049d-0f0a-f030-60e1609fc4c3@linux.intel.com>
Date:   Wed, 4 May 2022 16:47:54 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...el.com>
Cc:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] iommu/vt-d: Remove domain_update_iommu_snooping()

On 2022/5/3 05:36, Jacob Pan wrote:
> Hi BaoLu,
> 
> On Sun, 1 May 2022 19:24:33 +0800, Lu Baolu <baolu.lu@...ux.intel.com>
> wrote:
> 
>> The IOMMU force snooping capability is not required to be consistent
>> among all the IOMMUs anymore. Remove force snooping capability check
>> in the IOMMU hot-add path and domain_update_iommu_snooping() becomes
>> a dead code now.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 34 +---------------------------------
>>   1 file changed, 1 insertion(+), 33 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 3c1c228f9031..d5808495eb64 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -533,33 +533,6 @@ static void domain_update_iommu_coherency(struct
>> dmar_domain *domain) rcu_read_unlock();
>>   }
>>   
>> -static bool domain_update_iommu_snooping(struct intel_iommu *skip)
>> -{
>> -	struct dmar_drhd_unit *drhd;
>> -	struct intel_iommu *iommu;
>> -	bool ret = true;
>> -
>> -	rcu_read_lock();
>> -	for_each_active_iommu(iommu, drhd) {
>> -		if (iommu != skip) {
>> -			/*
>> -			 * If the hardware is operating in the scalable
>> mode,
>> -			 * the snooping control is always supported
>> since we
>> -			 * always set PASID-table-entry.PGSNP bit if the
>> domain
>> -			 * is managed outside (UNMANAGED).
>> -			 */
>> -			if (!sm_supported(iommu) &&
>> -			    !ecap_sc_support(iommu->ecap)) {
>> -				ret = false;
>> -				break;
>> -			}
>> -		}
>> -	}
>> -	rcu_read_unlock();
>> -
>> -	return ret;
>> -}
>> -
>>   static int domain_update_iommu_superpage(struct dmar_domain *domain,
>>   					 struct intel_iommu *skip)
>>   {
>> @@ -3593,12 +3566,7 @@ static int intel_iommu_add(struct dmar_drhd_unit
>> *dmaru) iommu->name);
>>   		return -ENXIO;
>>   	}
>> -	if (!ecap_sc_support(iommu->ecap) &&
>> -	    domain_update_iommu_snooping(iommu)) {
>> -		pr_warn("%s: Doesn't support snooping.\n",
>> -			iommu->name);
>> -		return -ENXIO;
>> -	}
>> +
> Maybe I missed earlier patches, so this bit can also be deleted?
> 
> struct dmar_domain {
> 	u8 iommu_snooping: 1;		/* indicate snooping control
> feature */

It has been cleaned up by below commit:

71cfafda9c9b vfio: Move the Intel no-snoop control off of IOMMU_CACHE

> 
>>   	sp = domain_update_iommu_superpage(NULL, iommu) - 1;
>>   	if (sp >= 0 && !(cap_super_page_val(iommu->cap) & (1 << sp))) {
>>   		pr_warn("%s: Doesn't support large page.\n",
> 
> 
> Thanks,
> 
> Jacob

Best regards,
baolu