linux-kernel - Re: [PATCH v4 2/5] iommu/vt-d: Remove the pasid present check in prq_event

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Message-ID: <e4460731-a13f-479d-b092-649123fe079f@linux.intel.com>
Date: Thu, 31 Oct 2024 11:42:24 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joel Granados <joel.granados@...nel.org>
Cc: Yi Liu <yi.l.liu@...el.com>, David Woodhouse <dwmw2@...radead.org>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>,
 Kevin Tian <kevin.tian@...el.com>, Klaus Jensen <its@...elevant.dk>,
 linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
 Klaus Jensen <k.jensen@...sung.com>
Subject: Re: [PATCH v4 2/5] iommu/vt-d: Remove the pasid present check in
 prq_event_thread

On 10/30/24 22:28, Joel Granados wrote:
>>    /*
>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
>> index 078d1e32a24e..ff88f31053d1 100644
>> --- a/drivers/iommu/intel/svm.c
>> +++ b/drivers/iommu/intel/svm.c
>> @@ -304,9 +304,6 @@ void intel_drain_pasid_prq(struct device *dev, u32
>> pasid)
>>           int qdep;
>>
>>           info = dev_iommu_priv_get(dev);
>> -       if (WARN_ON(!info || !dev_is_pci(dev)))
>> -               return;
> Did you mean to take out both checks?:
>    1. The info pointer check
>    2. the dev_is_pci check
> 
> I can understand the dev_is_pci check, but we should definitely take
> action if info is NULL. Right?

WARN_ON(!info) is duplicate as far as I can see. Accessing
info->pri_enable when info is NULL will cause a null pointer dereference
warning. This appears irrelevant to this patch though.

> 
>> -
>>           if (!info->pri_enabled)
>>                   return;
>>
>> Generally, intel_drain_pasid_prq() should be called if
>>
>> - a translation is removed from a pasid entry; and
> This is the path that is already mentiond
> 
>> - PRI on this device is enabled.
> And this path is:
>    -> intel_iommu_enable_iopf
>      -> context_flip_pri
>        -> intel_context_flush_present
>          -> qi_flush_pasid_cache
> 
> Right?

Sorry that I didn't make it clear. It should be "PRI on this device was
enabled", a.k.a. info->pri_enabled is true. I didn't meant to say in the
PRI enabling path.

--
baolu