[PATCH] x86/msi: always propagate MSI writes when not in active system mode

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Relax the limitation on MSI register writes, and only apply it when the
system is in active state.  For example AMD IOMMU drivers rely on using
set_msi_affinity() to force an MSI register write on resume from
suspension.

The original patch intention was to reduce the number of MSI register
writes when the system is in active state.  Leave the other states to
always perform the writes, as it's safer given the existing code, and it's
expected to not make a difference performance wise.

For such propagation to work even when the IRT index is not updated the MSI
message must be adjusted in all success cases for AMD IOMMU, not just when
the index has been newly allocated.

Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: ('8e60d47cf011 x86/iommu: avoid MSI address and data writes if IRT index 
hasn't changed')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/msi.c                       | 9 +++++++++
 xen/drivers/passthrough/amd/iommu_intr.c | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
index 163ccf874720..8bb3bb18af61 100644
--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -189,6 +189,15 @@ static int write_msi_msg(struct msi_desc *entry, struct 
msi_msg *msg,
 {
     entry->msg = *msg;
 
+    if ( unlikely(system_state != SYS_STATE_active) )
+        /*
+         * Always propagate writes when not in the 'active' state.  The
+         * optimization to avoid the MSI address and data registers write is
+         * only relevant for runtime state, and drivers on resume (at least)
+         * rely on set_msi_affinity() to update the hardware state.
+         */
+        force = true;
+
     if ( iommu_intremap != iommu_intremap_off )
     {
         int rc;
diff --git a/xen/drivers/passthrough/amd/iommu_intr.c 
b/xen/drivers/passthrough/amd/iommu_intr.c
index 9abdc38053d7..08766122b421 100644
--- a/xen/drivers/passthrough/amd/iommu_intr.c
+++ b/xen/drivers/passthrough/amd/iommu_intr.c
@@ -546,7 +546,7 @@ int cf_check amd_iommu_msi_msg_update_ire(
     rc = update_intremap_entry_from_msi_msg(iommu, bdf, nr,
                                             &msi_desc->remap_index,
                                             msg, &data);
-    if ( rc > 0 )
+    if ( rc >= 0 )
     {
         for ( i = 1; i < nr; ++i )
             msi_desc[i].remap_index = msi_desc->remap_index + i;
-- 
2.48.1