On Mon, Jan 13, 2025 at 11:25:58AM +0100, Roger Pau Monné wrote: > On Fri, Jan 10, 2025 at 04:30:57PM -0600, Bjorn Helgaas wrote: > > On Fri, Jan 10, 2025 at 03:01:50PM +0100, Roger Pau Monne wrote: > > > Setting pci_msi_ignore_mask inhibits the toggling of the mask bit for both MSI > > > and MSI-X entries globally, regardless of the IRQ chip they are using. Only > > > Xen sets the pci_msi_ignore_mask when routing physical interrupts over event > > > channels, to prevent PCI code from attempting to toggle the maskbit, as it's > > > Xen that controls the bit. > > > > > > However, the pci_msi_ignore_mask being global will affect devices that use MSI > > > interrupts but are not routing those interrupts over event channels (not using > > > the Xen pIRQ chip). One example is devices behind a VMD PCI bridge. In that > > > scenario the VMD bridge configures MSI(-X) using the normal IRQ chip (the pIRQ > > > one in the Xen case), and devices behind the bridge configure the MSI entries > > > using indexes into the VMD bridge MSI table. The VMD bridge then demultiplexes > > > such interrupts and delivers to the destination device(s). Having > > > pci_msi_ignore_mask set in that scenario prevents (un)masking of MSI entries > > > for devices behind the VMD bridge. > > > > > > Move the signaling of no entry masking into the MSI domain flags, as that > > > allows setting it on a per-domain basis. Set it for the Xen MSI domain that > > > uses the pIRQ chip, while leaving it unset for the rest of the cases. > > > > > > Remove pci_msi_ignore_mask at once, since it was only used by Xen code, and > > > with Xen dropping usage the variable is unneeded. > > > > > > This fixes using devices behind a VMD bridge on Xen PV hardware domains. > > > > Wrap to fit in 75 columns. > > > > The first two patches talk about devices behind VMD not being usable > > for Xen, but this one says they now work. > > Sorry, let me try to clarify: > > Devices behind a VMD bridge are not known to Xen, however that doesn't > mean Linux cannot use them. That's what this series achieves. By > inhibiting the usage of VMD_FEAT_CAN_BYPASS_MSI_REMAP and the removal > of the pci_msi_ignore_mask bodge devices behind a VMD bridge do work > fine when use from a Linux Xen hardware domain. That's the whole > point of the series. > > > But this doesn't undo the > > code changes or comments added by the first two, so the result is a > > bit confusing (probably because I know nothing about Xen). > > All patches are needed. There's probably some confusion about devices > behind a VMD bridge not being known by Xen vs not being usable by > Linux running under Xen as a hardware domain. > > With all three patches applied devices behind a VMD bridge work under > Linux with Xen. There's certainly confusion in *my* mind because I don't know enough about Xen to understand the subtlety about devices behind VMD not being known by Xen but still being usable by Linux running under Xen. Bjorn
