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spapr: don't initialize PATB entry if max-cpu-compat < power9 

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 <lvivier@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Laurent Vivier 2017-12-14 19:09:48 +01:00 committed by David Gibson
parent 4f441474c6
commit 1481fe5fcf
1 changed files with 4 additions and 2 deletions
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6
hw/ppc/spapr.c
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@ -1466,7 +1466,10 @@ static void spapr_machine_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. */
@ -1525,7 +1528,6 @@ static void spapr_machine_reset(void)
g_free(fdt);
/* 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;