Re: [PATCH v3 0/3] uio: add MSI/MSI-X support to uio_pci_generic driver

[Vlad Zolotarov]

On 10/06/15 17:30, Michael S. Tsirkin wrote:
> On Tue, Oct 06, 2015 at 11:37:59AM +0300, Vlad Zolotarov wrote:
> > Bus mastering is easily enabled from the user space (taken from DPDK code):
> >
> > static int
> > pci_uio_set_bus_master(int dev_fd)
> > {
> > 	uint16_t reg;
> > 	int ret;
> >
> > 	ret = pread(dev_fd, &reg, sizeof(reg), PCI_COMMAND);
> > 	if (ret != sizeof(reg)) {
> > 		RTE_LOG(ERR, EAL,
> > 			"Cannot read command from PCI config space!\n");
> > 		return -1;
> > 	}
> >
> > 	/* return if bus mastering is already on */
> > 	if (reg & PCI_COMMAND_MASTER)
> > 		return 0;
> >
> > 	reg |= PCI_COMMAND_MASTER;
> >
> > 	ret = pwrite(dev_fd, &reg, sizeof(reg), PCI_COMMAND);
> > 	if (ret != sizeof(reg)) {
> > 		RTE_LOG(ERR, EAL,
> > 			"Cannot write command to PCI config space!\n");
> > 		return -1;
> > 	}
> >
> > 	return 0;
> > }
> >
> > So, this is a non-issue. ;)
> There might be valid reasons for DPDK to do this, e.g. if using VFIO.

Michael, I'm afraid u are missing the main point here - the code above 
destroys all your long arguments. U can't possibly prevent the root-user 
from enabling the device bus mastering. And as me and other people on 
this thread have already mentioned MSI and MSI-X device configuration is 
controlled from the device BAR, thus may not be prevented too.


> I'm guessing it doesn't enable MSI though, does it?

Again, enabling MSI is a matter of a trivial patch configuring device 
registers on the device BAR.

>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/