On Wed, Apr 27, 2016 at 08:43:26PM +0800, Yongji Xie wrote:
> 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 changelog is ambiguous. It's possible that there is hardware
that *supports* IRQ remapping, but does not actually *do* IRQ
remapping. For example, an IRQ remapping capability may be present
but not enabled.
I think your intent is to set this flag only when MSI remapping is
actually *enabled* for all devices on the bus.
I'd also like to know exactly what protection is implied by
PCI_BUS_FLAGS_MSI_REMAP and IOMMU_CAP_INTR_REMAP. I guess it means a
device can only generate MSIs to a certain set of CPUs? I assume the
remapping hardware only checks the target address, not the data being
written?
> 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 in this patch so that we can use
> a universal flag to test this capability on PCI side for
> different archs.
>
> [1] http://www.spinics.net/lists/kvm/msg130256.html
>
> Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
> ---
> include/linux/pci.h | 1 +
> 1 file changed, 1 insertion(+)
>
> 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 */
> --
> 1.7.9.5
>
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