linux-kernel - RE: [PATCH v9 04/11] iommu: Add sva iommu

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Date:   Tue, 28 Jun 2022 08:50:16 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>
CC:     Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>
Subject: RE: [PATCH v9 04/11] iommu: Add sva iommu_domain support

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 28, 2022 1:41 PM
> >
> >>   struct iommu_domain {
> >>   	unsigned type;
> >>   	const struct iommu_domain_ops *ops;
> >>   	unsigned long pgsize_bitmap;	/* Bitmap of page sizes in use */
> >> -	iommu_fault_handler_t handler;
> >> -	void *handler_token;
> >>   	struct iommu_domain_geometry geometry;
> >>   	struct iommu_dma_cookie *iova_cookie;
> >> +	union {
> >> +		struct {	/* IOMMU_DOMAIN_DMA */
> >> +			iommu_fault_handler_t handler;
> >> +			void *handler_token;
> >> +		};
> >
> > why is it DMA domain specific? What about unmanaged
> > domain? Unrecoverable fault can happen on any type
> > including SVA. Hence I think above should be domain type
> > agnostic.
> 
> The report_iommu_fault() should be replaced by the new
> iommu_report_device_fault(). Jean has already started this work.
> 
> https://lore.kernel.org/linux-iommu/Yo4Nw9QyllT1RZbd@myrica/
> 
> Currently this is only for DMA domains, hence Robin suggested to make it
> exclude with the SVA domain things.
> 
> https://lore.kernel.org/linux-iommu/f3170016-4d7f-e78e-db48-
> 68305f683349@....com/

Then it's worthy a comment that those two fields are for
some legacy fault reporting stuff and DMA type only.

> >
> >> +
> >> +	mutex_lock(&group->mutex);
> >> +	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain,
> >> GFP_KERNEL);
> >> +	if (curr)
> >> +		goto out_unlock;
> >
> > Need check xa_is_err(old).
> 
> Either
> 
> (1) old entry is a valid pointer, or

return -EBUSY in this case

> (2) xa_is_err(curr)

return xa_err(cur)

> 
> are failure cases. Hence, "curr == NULL" is the only check we need. Did
> I miss anything?
> 

But now you always return -EBUSY for all kinds of xa errors.