[Qemu-devel] [PATCH] spapr/xive: Sanity checks of OV5 during CAS

[Greg Kurz <groug@kaod.org>]

If a machine is started with ic-mode=xive but the guest only knows
about XICS, eg. an RHEL 7.6 guest, the kernel panics. This is
expected but a bit unfortunate since the crash doesn't provide
much information for the end user to guess what's happening.

Detect that during CAS and exit QEMU with a proper error message
instead, like it is already done for the MMU.

Even if this is less likely to happen, the opposite case of a guest
that only knows about XIVE would certainly fail all the same if the
machine is started with ic-mode=xics.

Also, the only valid values a guest can pass in byte 23 of OV5 during
CAS are 0b00 (XIVE legacy mode) and 0b01 (XIVE exploitation mode). Any
other value is a bug, at least with the current spec. Again, it does
not seem right to let the guest go on without a precise idea of the
interrupt mode it asked for.

Handle these cases as well.

Reported-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/ppc/spapr_hcall.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 6c16d2b12040..63a55614b83d 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1513,6 +1513,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
     bool guest_radix;
     Error *local_err = NULL;
     bool raw_mode_supported = false;
+    bool guest_xive;
 
     cas_pvr = cas_check_pvr(spapr, cpu, &addr, &raw_mode_supported, &local_err);
     if (local_err) {
@@ -1545,10 +1546,17 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
         error_report("guest requested hash and radix MMU, which is invalid.");
         exit(EXIT_FAILURE);
     }
+    if (spapr_ovec_test(ov5_guest, OV5_XIVE_BOTH)) {
+        error_report("guest requested an invalid interrupt mode");
+        exit(EXIT_FAILURE);
+    }
+
     /* The radix/hash bit in byte 24 requires special handling: */
     guest_radix = spapr_ovec_test(ov5_guest, OV5_MMU_RADIX_300);
     spapr_ovec_clear(ov5_guest, OV5_MMU_RADIX_300);
 
+    guest_xive = spapr_ovec_test(ov5_guest, OV5_XIVE_EXPLOIT);
+
     /*
      * HPT resizing is a bit of a special case, because when enabled
      * we assume an HPT guest will support it until it says it
@@ -1632,6 +1640,22 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
                                           ov5_updates) != 0);
     }
 
+    /*
+     * Ensure the guest asks for an interrupt mode we support; otherwise
+     * terminate the boot.
+     */
+    if (guest_xive) {
+        if (spapr->irq->ov5 == SPAPR_OV5_XIVE_LEGACY) {
+            error_report("Guest requested unavailable interrupt mode (XIVE)");
+            exit(EXIT_FAILURE);
+        }
+    } else {
+        if (spapr->irq->ov5 == SPAPR_OV5_XIVE_EXPLOIT) {
+            error_report("Guest requested unavailable interrupt mode (XICS)");
+            exit(EXIT_FAILURE);
+        }
+    }
+
     /*
      * Generate a machine reset when we have an update of the
      * interrupt mode. Only required when the machine supports both