Re: iwx 64-bit dma

Vitaliy Makkoveev <[email protected]> wrote:

> On Wed, Jul 29, 2026 at 04:22:51PM -0600, Theo de Raadt wrote:
> > Are _all models_ of this chipset safe?
> > 
> 
> I don't know about PCI versions of this device. Moreover, it uses 64
> bits DMA since  revision 1.198 of sys/dev/pci/if_iwx.c.


The chipset always uses 64 bit descriptors, but they always pointed
into 32-bit memory.

There is other hardware that has 64 bit descriptors but can only access
less than 64 bits, for example kettenis sent a mail a week ago about
something which does 48 bits (but on a platform which has all memory
below that line)

So we must still be certain.  The existance of 64 bit descriptors is
not conclusive.
 
> revision 1.198
> date: 2026/02/17 20:02:43;  author: kettenis;  state: Exp;  lines: +8 -7;  commi
> tid: zh15zLsr17Uwlskc;
> Sprinkle some BUS_DMA_64BIT; this hardware has no issues handling full
> 64-bit addresses.
> 
> ok stsp@
> 
> But later, bluhm@ introduced IFXF_MBUF_64BIT flag for interface
> descriptor. The 64 bits DMA will not be used if at least one interface
> was configured without this flag. It seems iwx(4) was forgotten like
> re(4).
> 
> revision 1.306
> date: 2026/06/23 14:40:40;  author: bluhm;  state: Exp;  lines: +30 -1; commiti
> d: stkeyyILuxfbNN6W;
> Allocate mbufs in high memory if only 64 bit DMA interfaces exist.
> 
> Mbufs on amd64 were allocated below 4 GB so that devices not capable
> of 64 bit DMA can access the memory.  Interface drivers use
> BUS_DMA_64BIT to allow the DMA layer doing 64 bit transfers.  Now
> flag interfaces with IFXF_MBUF_64BIT that are capable of 64 bit DMA
> on all their mbuf rings.
> 
> If only such interfaces exist in the system during amd64 boot,
> allocate mbufs and mbuf clusters also in high memory.  Other
> architectures may be limited to 32 bit memory anyway or use an
> IOMMU.  On riscv64 or arm64 busses may exists that support less
> than 64 bit, this will be handled later.
> 
> Hotplug devices that do not support 64 bit DMA will use bounce
> buffering.  By changing the flags in device drivers we can force
> bounce buffering and find missing calls to bus_dmamap_sync().
> 
> OK kettenis@ deraadt@
> 
> > > On Tue, Jul 28, 2026 at 10:31:10PM -0400, Brad Smith wrote:
> > > > iwx(4) works with 64-bit DMA.
> > > > 
> > > > Tested with
> > > > 
> > > > iwx0 at pci0 dev 20 function 3 "Intel Wi-Fi 6 AX201" rev 0x00
> > > > 
> > > > 
> > > 
> > > Yes, this flag is missing. ok mvs@
> > > 
> > > > Index: if_iwx.c
> > > > ===================================================================
> > > > RCS file: /cvs/src/sys/dev/pci/if_iwx.c,v
> > > > retrieving revision 1.229
> > > > diff -u -p -u -p -r1.229 if_iwx.c
> > > > --- if_iwx.c	28 May 2026 10:51:52 -0000	1.229
> > > > +++ if_iwx.c	24 Jul 2026 03:10:09 -0000
> > > > @@ -12671,6 +12671,7 @@ iwx_attach(struct device *parent, struct
> > > >  
> > > >  	ifp->if_softc = sc;
> > > >  	ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
> > > > +	ifp->if_xflags = IFXF_MBUF_64BIT;
> > > >  	ifp->if_ioctl = iwx_ioctl;
> > > >  	ifp->if_start = iwx_start;
> > > >  	ifp->if_watchdog = iwx_watchdog;
> > > > 
> > > 
>