> -----Original Message----- > From: David Laight <David.Laight@xxxxxxxxxx> > Sent: 29 August 2023 22:10 > To: 'Stefan Hajnoczi' <stefanha@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; Alex Williamson > <alex.williamson@xxxxxxxxxx>; Jason Gunthorpe <jgg@xxxxxxxx> > Subject: RE: [PATCH v2 0/3] vfio: use __aligned_u64 for ioctl structs > > From: Stefan Hajnoczi > > Sent: 29 August 2023 19:27 > > > > v2: > > - Rebased onto https://github.com/awilliam/linux-vfio.git next to get the > > vfio_iommu_type1_info pad field [Kevin] > > - Fixed min(minsz, sizeof(dmabuf)) -> min(dmabuf.argsz, sizeof(dmabuf)) [Jason, Kevin] > > You managed to use min_t() instead of fixing the types to match. > > > - Squashed Patch 3 (vfio_iommu_type1_info) into Patch 1 since it is trivial now > > that the padding field is already there. > > > > Jason Gunthorpe <jgg@xxxxxxxxxx> pointed out that u64 VFIO ioctl struct fields > > have architecture-dependent alignment. iommufd already uses __aligned_u64 to > > avoid this problem. > > > > See the __aligned_u64 typedef in <uapi/linux/types.h> for details on why it is > > a good idea for kernel<->user interfaces. > > > > This series modifies the VFIO ioctl structs to use __aligned_u64. Some of the > > changes preserve the existing memory layout on all architectures, so I put them > > together into the first patch. The remaining patches are for structs where > > explanation is necessary about why changing the memory layout does not break > > the uapi. > > But you are extending a field in the middle of the uapi structure. > This completely breaks any applications. I've had a closer look this morning. Your explanations aren't very good. The structures all have the 64bit fields on their natural boundary so the memory layout isn't really changed - just extra padding at the end. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
