linux-kernel - Re: [PATCH] iommu/vt-d: Fix to flush cache of PASID directory table

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Date:   Fri, 16 Jun 2023 09:37:45 +0800
From:   Yanfei Xu <yanfei.xu@...el.com>
To:     "Zhang, Tina" <tina.zhang@...el.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/vt-d: Fix to flush cache of PASID directory table


On 6/16/2023 7:43 AM, Zhang, Tina wrote:
> Hi,
>
>> -----Original Message-----
>> From: Yanfei Xu <yanfei.xu@...el.com>
>> Sent: Thursday, June 15, 2023 3:16 PM
>> To: dwmw2@...radead.org; baolu.lu@...ux.intel.com; joro@...tes.org;
>> will@...nel.org; robin.murphy@....com
>> Cc: iommu@...ts.linux.dev; linux-kernel@...r.kernel.org; Xu, Yanfei
>> <yanfei.xu@...el.com>
>> Subject: [PATCH] iommu/vt-d: Fix to flush cache of PASID directory table
>>
>> Even the PCI devices don't support pasid capability, PASID table is mandatory
>> for a PCI device in scalable mode. However flushing cache of pasid directory
>> table for these devices are not taken after pasid table is allocated as the "size"
>> of table is zero. Fix to assign it with a page size.
>>
>> Fixes: 194b3348bdbb ("iommu/vt-d: Fix PASID directory pointer coherency")
>> Signed-off-by: Yanfei Xu <yanfei.xu@...el.com>
>> ---
>>   drivers/iommu/intel/pasid.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c index
>> c5d479770e12..bde7df055865 100644
>> --- a/drivers/iommu/intel/pasid.c
>> +++ b/drivers/iommu/intel/pasid.c
>> @@ -115,7 +115,9 @@ int intel_pasid_alloc_table(struct device *dev)
>>   				  intel_pasid_max_id);
>>
>>   	size = max_pasid >> (PASID_PDE_SHIFT - 3);
>> -	order = size ? get_order(size) : 0;
>> +	if (!size)
>> +		size = PAGE_SIZE;
> How about merging the logic of the above few lines into this one:
> size = info->pasid_supported ? max_pasid >> (PASID_PDE_SHIFT - 3) : PAGE_SIZE;

Yes, it would be more intuitive. But the prerequisite is if we can
make sure that the value of max_pasid shifted is still greater than
0. I roughly went through the PCIE spec and didn't find out where
defines the smallest PASID value for the PCIE device.

Thanks,
Yanfei

> Though the logic is about the same, the suggested one seems more intuitive.
>
> Regards,
> -Tina
>
>> +	order = get_order(size);
>>   	pages = alloc_pages_node(info->iommu->node,
>>   				 GFP_KERNEL | __GFP_ZERO, order);
>>   	if (!pages) {
>> --
>> 2.34.1
>>