| Message ID | 1460977120-29367-1-git-send-email-xyjxie@linux.vnet.ibm.com |
|---|---|
| State | Changes Requested |
| Headers | show |
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. 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. David
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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/pci.h b/include/linux/pci.h index 27df4a6..d619228 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -193,6 +193,7 @@ typedef unsigned short __bitwise pci_bus_flags_t; enum pci_bus_flags { PCI_BUS_FLAGS_NO_MSI = (__force pci_bus_flags_t) 1, PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2, + PCI_BUS_FLAGS_MSI_REMAP = (__force pci_bus_flags_t) 4, }; /* These values come from the PCI Express Spec */
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. There is a existing flag for this in the IOMMU space: enum iommu_cap { IOMMU_CAP_CACHE_COHERENCY, ---> IOMMU_CAP_INTR_REMAP, IOMMU_CAP_NOEXEC, }; and Eric also posted a patchset [1] to abstract this capability on MSI controller side for ARM. But it would make sense to have a more common flag like PCI_BUS_FLAGS_MSI_REMAP so that we can use a universal flag to test this capability for different archs on PCI side. [1] http://www.spinics.net/lists/kvm/msg130256.html Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com> --- include/linux/pci.h | 1 + 1 file changed, 1 insertion(+)