[Patch v4] x86: irq_comm: Add check for RH bit in kvm_set_msi_irq

[James Sullivan <sullivan.james.f@gmail.com>]

(Correction of a rather obvious and embarrassing logical error in v3).

This patch adds a check for RH=1 in kvm_set_msi_irq. Currently the
DM bit is the only thing used to decide irq->dest_mode (logical when DM
set, physical when unset). Documentation indicates that the DM bit will
be 'ignored' when the RH bit is unset, and physical destination mode is
used in this case.

Fixed this to set irq->dest_mode to APIC_DEST_LOGICAL just in case both
RH=1/DM=1.

This patch doesn't completely handle RH=1; if RH=1 then the delivery will behave
as in low priority mode (deliver the interrupt to only the lowest priority processor),
but the delivery mode may still used to specify the semantics of the delivery beyond
its destination.

I will be trying and comparing a few options to handle this fully (extension of
struct kvm_lapic_irq, introduction of MSI specific delivery functions or helpers,
etc) and hope to have some patches to show in the near future.


Signed-off-by: James Sullivan <sullivan.james.f@gmail.com>
---
Changes since v2:
    * Added one time warning message when RH=1
    * Documented conflict between RH=1 and delivery mode
    * Tidied code to check RH=1/DM=1 (remove bool phys, use if/else)
Changes since v3:
    * Fixed logical error in RH=1/DM=1 check
    * Aligned quotation blocks in multiline pr_warn_once argument

 arch/x86/kvm/irq_comm.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 72298b3..9514fed 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -103,12 +103,24 @@ static inline void kvm_set_msi_irq(struct kvm_kernel_irq_routing_entry *e,
 			MSI_ADDR_DEST_ID_MASK) >> MSI_ADDR_DEST_ID_SHIFT;
 	irq->vector = (e->msi.data &
 			MSI_DATA_VECTOR_MASK) >> MSI_DATA_VECTOR_SHIFT;
-	irq->dest_mode = (1 << MSI_ADDR_DEST_MODE_SHIFT) & e->msi.address_lo;
+	/*
+	 * TODO Deal with RH bit of MSI message address
+	 *  IF RH=1, then MSI delivers only to the processor with the
+	 *  lowest interrupt priority among processors that can receive
+	 *  the interrupt.
+	 */
+	if ((e->msi.address_lo & MSI_ADDR_REDIRECTION_LOWPRI) &&
+			(e->msi.address_lo & MSI_ADDR_DEST_MODE_LOGICAL))
+		irq->dest_mode = APIC_DEST_LOGICAL;
+	else
+		irq->dest_mode = APIC_DEST_PHYSICAL;
 	irq->trig_mode = (1 << MSI_DATA_TRIGGER_SHIFT) & e->msi.data;
 	irq->delivery_mode = e->msi.data & 0x700;
+	if (e->msi.address_lo & MSI_ADDR_REDIRECTION_LOWPRI)
+		pr_warn_once("KVM may not correctly deliver MSIs "
+			     "with RH set.\n");
 	irq->level = 1;
 	irq->shorthand = 0;
-	/* TODO Deal with RH bit of MSI message address */
 }

 int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
-- 
2.3.1