[PATCH v4 1/3] x86/vmx: fix posted interrupts usage of msi_desc->msg field

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

The current usage of msi_desc->msg in vmx_pi_update_irte() will make the
field contain a translated MSI message, instead of the expected
untranslated one.  This breaks dump_msi(), that use the data in
msi_desc->msg to print the interrupt details.

Fix this by introducing a dummy local msi_msg, and use it with
iommu_update_ire_from_msi().  vmx_pi_update_irte() relies on the MSI
message not changing, so there's no need to propagate the resulting msi_msg
to the hardware, and the contents can be ignored.

Fixes: a5e25908d18d ('VT-d: introduce new fields in msi_desc to track binding 
with guest interrupt')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v3:
 - New in this version.
---
 xen/arch/x86/hvm/vmx/vmx.c     | 9 ++++++++-
 xen/arch/x86/include/asm/msi.h | 2 +-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 0241303b4bf4..c407513af624 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -396,6 +396,13 @@ static int cf_check vmx_pi_update_irte(const struct vcpu 
*v,
     const struct pi_desc *pi_desc = v ? &v->arch.hvm.vmx.pi_desc : NULL;
     struct irq_desc *desc;
     struct msi_desc *msi_desc;
+    /*
+     * vmx_pi_update_irte() relies on the IRTE already being setup, and just
+     * updates the guest vector, but not the other IRTE fields.  As such the
+     * contents of msg are not consumed by iommu_update_ire_from_msi().  Even
+     * if not consumed, zero the contents to avoid possible stack leaks.
+     */
+    struct msi_msg msg = {};
     int rc;
 
     desc = pirq_spin_lock_irq_desc(pirq, NULL);
@@ -415,7 +422,7 @@ static int cf_check vmx_pi_update_irte(const struct vcpu *v,
 
     ASSERT_PDEV_LIST_IS_READ_LOCKED(msi_desc->dev->domain);
 
-    return iommu_update_ire_from_msi(msi_desc, &msi_desc->msg);
+    return iommu_update_ire_from_msi(msi_desc, &msg);
 
  unlock_out:
     spin_unlock_irq(&desc->lock);
diff --git a/xen/arch/x86/include/asm/msi.h b/xen/arch/x86/include/asm/msi.h
index 378b85ee947b..975d0f26b35d 100644
--- a/xen/arch/x86/include/asm/msi.h
+++ b/xen/arch/x86/include/asm/msi.h
@@ -124,7 +124,7 @@ struct msi_desc {
     int irq;
     int remap_index;         /* index in interrupt remapping table */
 
-    struct msi_msg msg;      /* Last set MSI message */
+    struct msi_msg msg;      /* Last set MSI message (untranslated) */
 };
 
 /*
-- 
2.48.1