linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Correctly check format of page table in debugfs

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Message-ID: <8d09da43-d0dd-9dff-0cb3-aa93448a7e60@linux.intel.com>
Date:   Thu, 25 Jul 2019 09:40:10 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, "Raj, Ashok" <ashok.raj@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH 1/1] iommu/vt-d: Correctly check format of page table in
 debugfs

Hi Sai,

On 7/22/19 1:21 PM, Prakhya, Sai Praneeth wrote:
> Hi Allen,
> 
>> diff --git a/drivers/iommu/intel-iommu-debugfs.c b/drivers/iommu/intel-
>> iommu-debugfs.c
>> index 73a552914455..e31c3b416351 100644
>> --- a/drivers/iommu/intel-iommu-debugfs.c
>> +++ b/drivers/iommu/intel-iommu-debugfs.c
>> @@ -235,7 +235,7 @@ static void ctx_tbl_walk(struct seq_file *m, struct
>> intel_iommu *iommu, u16 bus)
>>   		tbl_wlk.ctx_entry = context;
>>   		m->private = &tbl_wlk;
>>
>> -		if (pasid_supported(iommu) && is_pasid_enabled(context)) {
>> +		if (dmar_readq(iommu->reg + DMAR_RTADDR_REG) &
>> DMA_RTADDR_SMT) {
> 
> Thanks for adding this, I do believe this is a good addition but I also think that we might
> need "is_pasid_enabled()" as well. It checks if PASIDE bit in context entry is enabled or not.
> 
> I am thinking that even though DMAR might be using scalable root and context table, the entry
> itself should have PASIDE bit set. Did I miss something here?

No matter the PASIDE bit set or not, IOMMU always uses the scalable mode
page table if scalable mode is enabled. If PASIDE is set, requests with
PASID will be handled. Otherwise, requests with PASID will be blocked
(but request without PASID will always be handled).

We are dumpling the page table of the IOMMU, so we only care about what
page table format it is using. Do I understand it right>

Best regards,
Baolu

> 
> And I also think a macro would be better so that it could reused elsewhere (if need be).
> 
> Regards,
> Sai
>