On 2016/4/18 19:30, David Laight wrote:
From: Yongji Xie
Sent: 18 April 2016 11:59
We introduce a new pci_bus_flags, PCI_BUS_FLAGS_MSI_REMAP
which indicates all devices on the bus are protected by the
hardware which supports IRQ remapping(intel naming).
This flag will be used to know whether it's safe to expose
MSI-X tables of PCI BARs to userspace. Because the capability
of IRQ remapping can guarantee the PCI device cannot trigger
MSIs that correspond to interrupt IDs of other devices.
I'm worried that this entire series is going to break drivers
for existing hardware.
I understand some of the reasoning for 'vm pass through' configurations,
but there will be PCIe devices out there that have the MSI-X tables
in the same BAR as other device registers.
If you are lucky nothing else is in the same 4k area, but I wouldn't
assume it.
Thanks for your comments. But I didn't get your point here.
Why will exposing MSI-X table to userspace break the driver
for hardware which have the MSI-X tables in the same BAR as
other device registers? Could you give me more details?
The reason why we want to mmap MSI-X table is that there
may be some other critical device registers in the same page
as the MSI-X table. We prefer to handle the mmio access to
these registers in guest rather than in QEMU. So we would
like to see there is something else in the same 4k/64k area.
In any case, if the hardware can't police the card's master transfers
there is nothing to stop a different bus master block on the card
from raising MSI-X interrupts - they are just a PCIe write.
So all you are doing is raising the bar slightly and giving a very false
sense of security.
Do you mean we can request a DMA to the target address
area that raises MSI-X interrupts? But for PPC64 with IODA
bridge, this invalid PCIe write will be prevented on PHB before
raising MSI-X interrupt. And I think the capability of interrupt
remapping or ITS can also do the same thing. If hardware didn't
support this, we would not expose MSI-X table in my patch.
Thanks,
Yongji
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
