linux-kernel - Re: [PATCH v2 1/1] iommu/vt-d: Make intel_iommu_drain_pasid

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Message-ID: <3cca401b-e274-471b-8910-bb30873ead1b@intel.com>
Date: Tue, 21 Jan 2025 15:01:35 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, Kevin Tian
	<kevin.tian@...el.com>
CC: <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] iommu/vt-d: Make intel_iommu_drain_pasid_prq()
 cover faults for RID

On 2025/1/21 10:31, Lu Baolu wrote:
> This driver supports page faults on PCI RID since commit <9f831c16c69e>
> ("iommu/vt-d: Remove the pasid present check in prq_event_thread") by
> allowing the reporting of page faults with the pasid_present field cleared
> to the upper layer for further handling. The fundamental assumption here
> is that the detach or replace operations act as a fence for page faults.
> This implies that all pending page faults associated with a specific RID
> or PASID are flushed when a domain is detached or replaced from a device
> RID or PASID.
> 
> However, the intel_iommu_drain_pasid_prq() helper does not correctly
> handle faults for RID. This leads to faults potentially remaining pending
> in the iommu hardware queue even after the domain is detached, thereby
> violating the aforementioned assumption.
> 
> Fix this issue by extending intel_iommu_drain_pasid_prq() to cover faults
> for RID.
> 
> Fixes: 9f831c16c69e ("iommu/vt-d: Remove the pasid present check in prq_event_thread")
> Cc: stable@...r.kernel.org
> Suggested-by: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> ---
>   drivers/iommu/intel/prq.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Change log:
> v2:
>   - Add check on page faults targeting RID.
> 
> v1: https://lore.kernel.org/linux-iommu/20250120080144.810455-1-baolu.lu@linux.intel.com/
> 
> diff --git a/drivers/iommu/intel/prq.c b/drivers/iommu/intel/prq.c
> index c2d792db52c3..064194399b38 100644
> --- a/drivers/iommu/intel/prq.c
> +++ b/drivers/iommu/intel/prq.c
> @@ -87,7 +87,9 @@ void intel_iommu_drain_pasid_prq(struct device *dev, u32 pasid)
>   		struct page_req_dsc *req;
>   
>   		req = &iommu->prq[head / sizeof(*req)];
> -		if (!req->pasid_present || req->pasid != pasid) {
> +		if (req->rid != sid ||

Does intel-iommu driver managed pasid per-bdf? or global? If the prior one,
the rid check is needed even in the old time that does not PRIs in the RID
path.

> +		    (req->pasid_present && pasid != req->pasid) ||
> +		    (!req->pasid_present && pasid != IOMMU_NO_PASID)) {
>   			head = (head + sizeof(*req)) & PRQ_RING_MASK;
>   			continue;
>   		}

LGTM.

Reviewed-by: Yi Liu <yi.l.liu@...el.com>

-- 
Regards,
Yi Liu