target/ppc: 'PVR != host PVR' in KVM_SET_SREGS workaround
Commit d5fc133eed
("ppc: Rework CPU compatibility testing
across migration") changed the way cpu_post_load behaves with
the PVR setting, causing an unexpected bug in KVM-HV migrations
between hosts that are compatible (POWER8 and POWER8E, for example).
Even with pvr_match() returning true, the guest freezes right after
cpu_post_load. The reason is that the guest kernel can't handle a
different PVR value other that the running host in KVM_SET_SREGS.
In [1] it was discussed the possibility of a new KVM capability
that would indicate that the guest kernel can handle a different
PVR in KVM_SET_SREGS. Even if such feature is implemented, there is
still the problem with older kernels that will not have this capability
and will fail to migrate.
This patch implements a workaround for that scenario. If running
with KVM, check if the guest kernel does not have the capability
(named here as 'cap_ppc_pvr_compat'). If it doesn't, calls
kvmppc_is_pr() to see if the guest is running in KVM-HV. If all this
happens, set env->spr[SPR_PVR] to the same value as the current
host PVR. This ensures that we allow migrations with 'close enough'
PVRs to still work in KVM-HV but also makes the code ready for
this new KVM capability when it is done.
A new function called 'kvmppc_pvr_workaround_required' was created
to encapsulate the conditions said above and to avoid calling too
many kvm.c internals inside cpu_post_load.
[1] https://lists.gnu.org/archive/html/qemu-ppc/2017-06/msg00503.html
Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
[dwg: Fix for the case of using TCG on a PPC host]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
parent
b96919d765
commit
c363a37a45
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@ -90,6 +90,7 @@ static int cap_htm; /* Hardware transactional memory support */
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static int cap_mmu_radix;
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static int cap_mmu_hash_v3;
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static int cap_resize_hpt;
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static int cap_ppc_pvr_compat;
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static uint32_t debug_inst_opcode;
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@ -147,6 +148,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
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cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX);
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cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3);
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cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
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/*
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* Note: setting it to false because there is not such capability
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* in KVM at this moment.
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*
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* TODO: call kvm_vm_check_extension() with the right capability
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* after the kernel starts implementing it.*/
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cap_ppc_pvr_compat = false;
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if (!cap_interrupt_level) {
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fprintf(stderr, "KVM: Couldn't find level irq capability. Expect the "
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@ -2785,3 +2793,33 @@ void kvmppc_update_sdr1(target_ulong sdr1)
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run_on_cpu(cs, kvmppc_pivot_hpt_cpu, RUN_ON_CPU_TARGET_PTR(sdr1));
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}
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}
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/*
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* This is a helper function to detect a post migration scenario
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* in which a guest, running as KVM-HV, freezes in cpu_post_load because
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* the guest kernel can't handle a PVR value other than the actual host
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* PVR in KVM_SET_SREGS, even if pvr_match() returns true.
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*
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* If we don't have cap_ppc_pvr_compat and we're not running in PR
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* (so, we're HV), return true. The workaround itself is done in
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* cpu_post_load.
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*
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* The order here is important: we'll only check for KVM PR as a
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* fallback if the guest kernel can't handle the situation itself.
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* We need to avoid as much as possible querying the running KVM type
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* in QEMU level.
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*/
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bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu)
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{
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CPUState *cs = CPU(cpu);
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if (!kvm_enabled()) {
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return false;
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}
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if (cap_ppc_pvr_compat) {
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return false;
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}
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return !kvmppc_is_pr(cs->kvm_state);
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}
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@ -67,6 +67,7 @@ void kvmppc_check_papr_resize_hpt(Error **errp);
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int kvmppc_resize_hpt_prepare(PowerPCCPU *cpu, target_ulong flags, int shift);
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int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift);
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void kvmppc_update_sdr1(target_ulong sdr1);
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bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu);
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bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path);
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@ -9,6 +9,7 @@
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#include "mmu-hash64.h"
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#include "migration/cpu.h"
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#include "qapi/error.h"
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#include "kvm_ppc.h"
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static int cpu_load_old(QEMUFile *f, void *opaque, int version_id)
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{
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@ -249,6 +250,27 @@ static int cpu_post_load(void *opaque, int version_id)
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}
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}
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/*
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* If we're running with KVM HV, there is a chance that the guest
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* is running with KVM HV and its kernel does not have the
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* capability of dealing with a different PVR other than this
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* exact host PVR in KVM_SET_SREGS. If that happens, the
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* guest freezes after migration.
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*
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* The function kvmppc_pvr_workaround_required does this verification
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* by first checking if the kernel has the cap, returning true immediately
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* if that is the case. Otherwise, it checks if we're running in KVM PR.
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* If the guest kernel does not have the cap and we're not running KVM-PR
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* (so, it is running KVM-HV), we need to ensure that KVM_SET_SREGS will
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* receive the PVR it expects as a workaround.
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*
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*/
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#if defined(CONFIG_KVM)
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if (kvmppc_pvr_workaround_required(cpu)) {
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env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
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}
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#endif
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env->lr = env->spr[SPR_LR];
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env->ctr = env->spr[SPR_CTR];
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cpu_write_xer(env, env->spr[SPR_XER]);
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