linux-kernel - Re: [PATCH 1/3] iommu/vt-d: Set PGSNP bit in pasid table entry for sva binding

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Date:   Mon, 18 Apr 2022 19:28:28 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     baolu.lu@...ux.intel.com,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] iommu/vt-d: Set PGSNP bit in pasid table entry for
 sva binding

On 2022/4/18 14:56, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.intel.com>
>> Sent: Saturday, April 16, 2022 8:31 PM
>>
>> This field make the requests snoop processor caches irrespective of other
>> attributes in the request or other fields in paging structure entries
>> used to translate the request. The latest VT-d specification states that
>> this field is treated as Reserved(0) for implementations not supporting
>> Snoop Control (SC=0 in the Extended Capability Register). Hence add a
>> check in the code.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel/pasid.c | 2 +-
>>   drivers/iommu/intel/svm.c   | 1 +
>>   2 files changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
>> index f8d215d85695..9ca3c67a2058 100644
>> --- a/drivers/iommu/intel/pasid.c
>> +++ b/drivers/iommu/intel/pasid.c
>> @@ -625,7 +625,7 @@ int intel_pasid_setup_first_level(struct intel_iommu
>> *iommu,
>>   		}
>>   	}
>>
>> -	if (flags & PASID_FLAG_PAGE_SNOOP)
>> +	if ((flags & PASID_FLAG_PAGE_SNOOP) && ecap_sc_support(iommu-
>>> ecap))
>>   		pasid_set_pgsnp(pte);
> If the caller wants snoop for some reason is it correct to simply
> ignore the request when lacking of hw support? Suppose certain
> errno should be returned here...

Good catch. Perhaps I should make the cap check in a separated patch.

Best regards,
baolu