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[Qemu-devel] [PATCH 36/54] spapr: don't initialize PATB entry if max-cpu

From: Michael Roth
Subject: [Qemu-devel] [PATCH 36/54] spapr: don't initialize PATB entry if max-cpu-compat < power9
Date: Tue, 6 Feb 2018 13:14:57 -0600

From: Laurent Vivier <address@hidden>

if KVM is enabled and KVM capabilities MMU radix is available,
the partition table entry (patb_entry) for the radix mode is
initialized by default in ppc_spapr_reset().

It's a problem if we want to migrate the guest to a POWER8 host
while the kernel is not started to set the value to the one
expected for a POWER8 CPU.

The "-machine max-cpu-compat=power8" should allow to migrate
a POWER9 KVM host to a POWER8 KVM host, but because patb_entry
is set, the destination QEMU tries to enable radix mode on the
POWER8 host. This fails and cancels the migration:

    Process table config unsupported by the host
    error while loading state for instance 0x0 of device 'spapr'
    load of migration failed: Invalid argument

This patch doesn't set the PATB entry if the user provides
a CPU compatibility mode that doesn't support radix mode.

Signed-off-by: Laurent Vivier <address@hidden>
Signed-off-by: David Gibson <address@hidden>
(cherry picked from commit 1481fe5fcfeb7fcf3c1ebb9d8c0432e3e0188ccf)
Signed-off-by: Michael Roth <address@hidden>
 hw/ppc/spapr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 1ac7eb0f8c..66d0ed5256 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1440,7 +1440,10 @@ static void ppc_spapr_reset(void)
     /* Check for unknown sysbus devices */
     foreach_dynamic_sysbus_device(find_unknown_sysbus_device, NULL);
-    if (kvm_enabled() && kvmppc_has_cap_mmu_radix()) {
+    first_ppc_cpu = POWERPC_CPU(first_cpu);
+    if (kvm_enabled() && kvmppc_has_cap_mmu_radix() &&
+        ppc_check_compat(first_ppc_cpu, CPU_POWERPC_LOGICAL_3_00, 0,
+                         spapr->max_compat_pvr)) {
         /* If using KVM with radix mode available, VCPUs can be started
          * without a HPT because KVM will start them in radix mode.
          * Set the GR bit in PATB so that we know there is no HPT. */
@@ -1499,7 +1502,6 @@ static void ppc_spapr_reset(void)
     /* Set up the entry state */
-    first_ppc_cpu = POWERPC_CPU(first_cpu);
     first_ppc_cpu->env.gpr[3] = fdt_addr;
     first_ppc_cpu->env.gpr[5] = 0;
     first_cpu->halted = 0;

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