Legacy PIC (8259) cannot be supported for TDX VMs since TDX module
doesn't allow directly interrupt injection.  Using posted interrupts
for the PIC is not a viable option as the guest BIOS/kernel will not
do EOI for PIC IRQs, i.e. will leave the vIRR bit set.

Hence disable PIC for TDX VMs and error out if user wants PIC.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
---
 target/i386/kvm/tdx.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index 0eefd058f7a2..0d30506c2021 100644
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -383,6 +383,13 @@ static int tdx_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
         return -EINVAL;
     }
 
+    if (x86ms->pic == ON_OFF_AUTO_AUTO) {
+        x86ms->pic = ON_OFF_AUTO_OFF;
+    } else if (x86ms->pic == ON_OFF_AUTO_ON) {
+        error_setg(errp, "TDX VM doesn't support PIC");
+        return -EINVAL;
+    }
+
     if (!tdx_caps) {
         r = get_tdx_capabilities(errp);
         if (r) {
-- 
2.34.1

On Tue, Apr 01, 2025 at 09:01:47AM -0400, Xiaoyao Li wrote:
> Legacy PIC (8259) cannot be supported for TDX VMs since TDX module
> doesn't allow directly interrupt injection.  Using posted interrupts
> for the PIC is not a viable option as the guest BIOS/kernel will not
> do EOI for PIC IRQs, i.e. will leave the vIRR bit set.
> 
> Hence disable PIC for TDX VMs and error out if user wants PIC.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  target/i386/kvm/tdx.c | 7 +++++++
>  1 file changed, 7 insertions(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|