linux-kernel - Re: [PATCH RFC 08/11] iommu: Handle IO page faults directly

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Message-ID: <YjhjCsrcTNDsFRwm@myrica>
Date:   Mon, 21 Mar 2022 11:35:38 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 08/11] iommu: Handle IO page faults directly

On Sun, Mar 20, 2022 at 02:40:27PM +0800, Lu Baolu wrote:
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index c0966fc9b686..4f90b71c6f6e 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -27,6 +27,8 @@
>  #include <linux/cc_platform.h>
>  #include <trace/events/iommu.h>
>  
> +#include "iommu-sva-lib.h"
> +
>  static struct kset *iommu_group_kset;
>  static DEFINE_IDA(iommu_group_ida);
>  
> @@ -1177,10 +1179,9 @@ int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
>  	if (!param || !evt)
>  		return -EINVAL;
>  
> -	/* we only report device fault if there is a handler registered */
>  	mutex_lock(&param->lock);
>  	fparam = param->fault_param;
> -	if (!fparam || !fparam->handler) {
> +	if (!fparam) {
>  		ret = -EINVAL;
>  		goto done_unlock;
>  	}
> @@ -1198,7 +1199,11 @@ int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
>  		mutex_unlock(&fparam->lock);
>  	}
>  
> -	ret = fparam->handler(&evt->fault, fparam->data);
> +	if (fparam->handler)
> +		ret = fparam->handler(&evt->fault, fparam->data);
> +	else
> +		ret = iommu_queue_iopf(&evt->fault, fparam->data);
> +

I like the change, but we'll need to consolidate this, because now if the
driver registers a fault handler it disables IOPF. We could instead
prevent registration if an IOPF param is present. We could also just merge
fparam->handler but eventually I'd like to make IOPF fall back to the
fault handler registered by device driver, in case of invalid page faults.
I have a couple patches for this but am still missing some bits.

Thanks,
Jean

>  	if (ret && evt_pending) {
>  		mutex_lock(&fparam->lock);
>  		list_del(&evt_pending->list);
> -- 
> 2.25.1
>