linux-kernel - Re: [PATCH v8 06/10] iommufd: Add iommufd fault object

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Message-ID: <20240708162255.GA14050@ziepe.ca>
Date: Mon, 8 Jul 2024 13:22:55 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, Baolu Lu <baolu.lu@...ux.intel.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Joel Granados <j.granados@...sung.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 06/10] iommufd: Add iommufd fault object

On Fri, Jul 05, 2024 at 12:49:10AM +0000, Tian, Kevin wrote:

> > > > > > > +enum iommu_fault_type {
> > > > > > > +     IOMMU_FAULT_TYPE_HWPT_IOPF,
> > > > > > > +     IOMMU_FAULT_TYPE_VIOMMU_IRQ,
> > > > > > > +};
> > > > > > >
> > > > > > >    struct iommu_fault_alloc {
> > > > > > >        __u32 size;
> > > > > > >        __u32 flags;
> > > > > > > +     __u32 type;  /* enum iommu_fault_type */
> > > > > > >        __u32 out_fault_id;
> > > > > > >        __u32 out_fault_fd;
> > > > and need a new reserved field for alignment.
> > 
> > Hmm, what's the reason for enforcing a 64-bit alignment to an
> > all-u32 struct though? I thought we need a reserved field only
> > for padding. The struct iommu_ioas_alloc has three u32 members
> > for example?
> 
> yeah please ignore this comment.

Sometimes I encourage it so that people notice the if the structure is
changed later. Almost all structs here are 8 byte aligned. It is OK
like this too.

Jason