On Tue, 2024-12-03 at 10:41 -0800, Ramesh Thomas wrote: > Definitions of ioread64 and iowrite64 macros in asm/io.h called by vfio > pci implementations are enclosed inside check for CONFIG_GENERIC_IOMAP. > They don't get defined if CONFIG_GENERIC_IOMAP is defined. Include > linux/io-64-nonatomic-lo-hi.h to define iowrite64 and ioread64 macros > when they are not defined. io-64-nonatomic-lo-hi.h maps the macros to > generic implementation in lib/iomap.c. The generic implementation does > 64 bit rw if readq/writeq is defined for the architecture, otherwise it > would do 32 bit back to back rw. > > Note that there are two versions of the generic implementation that > differs in the order the 32 bit words are written if 64 bit support is > not present. This is not the little/big endian ordering, which is > handled separately. This patch uses the lo followed by hi word ordering > which is consistent with current back to back implementation in the > vfio/pci code. > > Signed-off-by: Ramesh Thomas <ramesh.thomas@xxxxxxxxx> > --- > drivers/vfio/pci/vfio_pci_rdwr.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c > index 66b72c289284..a0595c745732 100644 > --- a/drivers/vfio/pci/vfio_pci_rdwr.c > +++ b/drivers/vfio/pci/vfio_pci_rdwr.c > @@ -16,6 +16,7 @@ > #include <linux/io.h> > #include <linux/vfio.h> > #include <linux/vgaarb.h> > +#include <linux/io-64-nonatomic-lo-hi.h>> > > #include "vfio_pci_priv.h" > Getting from linux/io-64-nonatomic-lo-hi.h to the lib/iomap.c implementations is a bit of a wild goose chase but I convinced myself that it happens as you describe when GENERIC_IOMAP is set. Also makes sense to me to use the linux/io-64-nonatomic-lo-hi.h header for a generic fallback where the access order matches what vfio already does. I do wonder if this actually improves things for more than just x86. As far as I can see powerpc also uses GENERIC_IOMAP with POWERNV which is also 64 bit and also has users of vfio-pci. So adding Michael Ellerman for awareness. Thanks, Niklas
