[xen stable-4.20] x86/vmx: fix posted interrupts usage of msi_desc->msg field

[patchbot@xxxxxxx]

commit 74b40fe10582c0375afd3db97626a27094f4c0e5
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Mar 20 12:52:00 2025 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 20 12:52:00 2025 +0100

    x86/vmx: fix posted interrupts usage of msi_desc->msg field
    
    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.
    
    Additionally add a comment to clarify that msi_desc->msg must always
    contain the untranslated MSI message.
    
    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>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 30f0e55a79206702b4e82e86dad6b35033157858
    master date: 2025-03-12 13:32:30 +0100
---
 xen/arch/x86/hvm/vmx/vmx.c     | 4 +++-
 xen/arch/x86/include/asm/msi.h | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index eee1d4b47a..1373ef2787 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -396,6 +396,7 @@ 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;
+    struct msi_msg msg;
     int rc;
 
     desc = pirq_spin_lock_irq_desc(pirq, NULL);
@@ -410,12 +411,13 @@ static int cf_check vmx_pi_update_irte(const struct vcpu 
*v,
     }
     msi_desc->pi_desc = pi_desc;
     msi_desc->gvec = gvec;
+    msg = msi_desc->msg;
 
     spin_unlock_irq(&desc->lock);
 
     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 7f9e531f73..38367e2788 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) */
 };
 
 /*
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.20