On Wed, Mar 18, 2015 at 06:59:22PM -0600, James Sullivan wrote: > > > > The documentation states the following: > > > > * When RH is 0, the interrupt is directed to the processor listed in the > > Destination ID field. > > > > * If RH is 0, then the DM bit is ignored and the message is sent ahead > > independent of whether the physical or logical destination mode is used. > > > > However, from the POV of a device writing to memory to generate an MSI > > interrupt, there is no (or i can't see any) other information that > > can be used to infer logical or physical mode for the interrupt message. > > > > Before your patch: > > > > (dm, rh) = (0, 0) => irq->dest_mode = 0 > > (dm, rh) = (0, 1) => irq->dest_mode = 0 > > (dm, rh) = (1, 0) => irq->dest_mode = 1 > > (dm, rh) = (1, 1) => irq->dest_mode = 1 > > > > After your patch: > > > > (dm, rh) = (0, 0) => irq->dest_mode = 0 > > (dm, rh) = (0, 1) => irq->dest_mode = 0 > > (dm, rh) = (1, 0) => irq->dest_mode = 0 > > (dm, rh) = (1, 1) => irq->dest_mode = 1 > > > > > > Am i missing some explicit documentation that refers > > to (dm, rh) = (1, 0) => irq->dest_mode = 0 ? > > >From the IA32 manual (Vol. 3, 10.11.2): > > * When RH is 0, the interrupt is directed to the processor listed > in the Destination ID field. > * When RH is 1 and the physical destination mode is used, the Destination > ID field must not be set to FFH; it must point to a processor that is > present and enabled to receive the interrupt. > * When RH is 1 and the logical destination mode is active in a system using > a flat addressing model, the Destination ID field must be set so that bits > set to 1 identify processors that are present and enabled to receive the > interrupt. > * If RH is set to 1 and the logical destination mode is active in a system > using cluster addressing model, then Destination ID field must not be > set to FFH; the processors identified with this field must be present > and enabled to receive the interrupt. > > My interpretation of this is that RH=0 indicates that the Dest. ID field > contains an APIC ID, and as such destination mode is physical. When RH=1, > depending on the value of DM, we either use physical or logical dest mode. > The result of this is that logical dest mode is set just when RH=1/DM=1, > as far as I understand. > > > > > See native_compose_msi_msg: > > > > msg->address_lo = > > MSI_ADDR_BASE_LO | > > ((apic->irq_dest_mode == 0) ? > > MSI_ADDR_DEST_MODE_PHYSICAL : > > MSI_ADDR_DEST_MODE_LOGICAL) | > > ((apic->irq_delivery_mode != dest_LowestPrio) ? > > MSI_ADDR_REDIRECTION_CPU : > > MSI_ADDR_REDIRECTION_LOWPRI) | > > MSI_ADDR_DEST_ID(dest); > > > > > > So it does configure DM = MSI_ADDR_DEST_MODE_LOGICAL > > and RH = MSI_ADDR_REDIRECTION_LOWPRI. > > > > ...and yet this is a good counterexample against my argument :) > > What I think I'll do is revert this particular change so that dest_mode is > set independently of RH. While I'm not entirely convinced that this is the > intended interpretation, Where would the logical/physical information come from, if not from the DM bit ? > I do think that consistency with the existing logic > is probably desirable for the time being. If I can get closure on the matter > I'll re-submit that change, but for the time being I will undo it. > > -James -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
