linux-kernel - Re: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND

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Date:   Wed, 22 Sep 2021 20:01:16 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Liu Yi L <yi.l.liu@...el.com>, hch@....de, jasowang@...hat.com,
        joro@...tes.org, jean-philippe@...aro.org, kevin.tian@...el.com,
        parav@...lanox.com, lkml@...ux.net, pbonzini@...hat.com,
        lushenming@...wei.com, eric.auger@...hat.com, corbet@....net,
        ashok.raj@...el.com, yi.l.liu@...ux.intel.com,
        jun.j.tian@...el.com, hao.wu@...el.com, dave.jiang@...el.com,
        jacob.jun.pan@...ux.intel.com, kwankhede@...dia.com,
        robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        david@...son.dropbear.id.au, nicolinc@...dia.com
Subject: Re: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND_IOMMUFD

On Wed, Sep 22, 2021 at 03:01:01PM -0600, Alex Williamson wrote:
> On Tue, 21 Sep 2021 14:29:39 -0300
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > On Sun, Sep 19, 2021 at 02:38:36PM +0800, Liu Yi L wrote:
> > > +struct vfio_device_iommu_bind_data {
> > > +	__u32	argsz;
> > > +	__u32	flags;
> > > +	__s32	iommu_fd;
> > > +	__u64	dev_cookie;  
> > 
> > Missing explicit padding
> > 
> > Always use __aligned_u64 in uapi headers, fix all the patches.
> 
> We don't need padding or explicit alignment if we just swap the order
> of iommu_fd and dev_cookie.  Thanks,

Yes, the padding should all be checked and minimized

But it is always good practice to always use __aligned_u64 in the uapi
headers just in case someone messes it up someday - it prevents small
mistakes from becoming an ABI mess.

Jason