[PATCH v2 1/2] iommu/amd: Don't block updates to GATag if guest mode is on

[Joao Martins <joao.m.martins@oracle.com>]

On KVM GSI routing table updates, specially those where they have vIOMMUs
with interrupt remapping enabled (to boot >255vcpus setups without relying
on KVM_FEATURE_MSI_EXT_DEST_ID), a VMM may update the backing VF MSIs
with a new VCPU affinity.

On AMD with AVIC enabled, the new vcpu affinity info is updated via:
	avic_pi_update_irte()
		irq_set_vcpu_affinity()
			amd_ir_set_vcpu_affinity()
				amd_iommu_{de}activate_guest_mode()

Where the IRTE[GATag] is updated with the new vcpu affinity. The GATag
contains VM ID and VCPU ID, and is used by IOMMU hardware to signal KVM
(via GALog) when interrupt cannot be delivered due to vCPU is in
blocking state.

The issue is that amd_iommu_activate_guest_mode() will essentially
only change IRTE fields on transitions from non-guest-mode to guest-mode
and otherwise returns *with no changes to IRTE* on already configured
guest-mode interrupts. To the guest this means that the VF interrupts
remain affined to the first vCPU they were first configured, and guest
will be unable to either VF interrupts and receive messages like this
from spuruious interrupts (e.g. from waking the wrong vCPU in GALog):

[  167.759472] __common_interrupt: 3.34 No irq handler for vector
[  230.680927] mlx5_core 0000:00:02.0: mlx5_cmd_eq_recover:247:(pid
3122): Recovered 1 EQEs on cmd_eq
[  230.681799] mlx5_core 0000:00:02.0:
wait_func_handle_exec_timeout:1113:(pid 3122): cmd[0]: CREATE_CQ(0x400)
recovered after timeout
[  230.683266] __common_interrupt: 3.34 No irq handler for vector

Given the fact that amd_ir_set_vcpu_affinity() uses
amd_iommu_activate_guest_mode() underneath it essentially means that VCPU
affinity changes of IRTEs are nops. Fix it by dropping the check for
guest-mode at amd_iommu_activate_guest_mode(). Same thing is applicable to
amd_iommu_deactivate_guest_mode() although, even if the IRTE doesn't change
underlying DestID on the host, the VFIO IRQ handler will still be able to
poke at the right guest-vCPU.

Fixes: b9c6ff94e43a ("iommu/amd: Re-factor guest virtual APIC (de-)activation code")
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 drivers/iommu/amd/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 5a505ba5467e..bf3ebc9d6cde 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -3485,7 +3485,7 @@ int amd_iommu_activate_guest_mode(void *data)
 	u64 valid;
 
 	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
-	    !entry || entry->lo.fields_vapic.guest_mode)
+	    !entry)
 		return 0;
 
 	valid = entry->lo.fields_vapic.valid;
-- 
2.17.2