| Message ID | 20170809204346.5220-1-danielhb@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Aug 09, 2017 at 05:43:46PM -0300, Daniel Henrique Barboza wrote: > 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> Ugly, but necessary. Applied to ppc-for-2.10. > --- > target/ppc/kvm.c | 34 ++++++++++++++++++++++++++++++++++ > target/ppc/kvm_ppc.h | 1 + > target/ppc/machine.c | 22 ++++++++++++++++++++++ > 3 files changed, 57 insertions(+) > > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c > index 8571379..fb3ee43 100644 > --- a/target/ppc/kvm.c > +++ b/target/ppc/kvm.c > @@ -90,6 +90,7 @@ static int cap_htm; /* Hardware transactional memory support */ > static int cap_mmu_radix; > static int cap_mmu_hash_v3; > static int cap_resize_hpt; > +static int cap_ppc_pvr_compat; > > static uint32_t debug_inst_opcode; > > @@ -147,6 +148,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX); > cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3); > cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT); > + /* > + * Note: setting it to false because there is not such capability > + * in KVM at this moment. > + * > + * TODO: call kvm_vm_check_extension() with the right capability > + * after the kernel starts implementing it.*/ > + cap_ppc_pvr_compat = false; > > if (!cap_interrupt_level) { > fprintf(stderr, "KVM: Couldn't find level irq capability. Expect the " > @@ -2785,3 +2793,29 @@ void kvmppc_update_sdr1(target_ulong sdr1) > run_on_cpu(cs, kvmppc_pivot_hpt_cpu, RUN_ON_CPU_TARGET_PTR(sdr1)); > } > } > + > +/* > + * This is a helper function to detect a post migration scenario > + * in which a guest, running as KVM-HV, freezes in cpu_post_load because > + * the guest kernel can't handle a PVR value other than the actual host > + * PVR in KVM_SET_SREGS, even if pvr_match() returns true. > + * > + * If we don't have cap_ppc_pvr_compat and we're not running in PR > + * (so, we're HV), return true. The workaround itself is done in > + * cpu_post_load. > + * > + * The order here is important: we'll only check for KVM PR as a > + * fallback if the guest kernel can't handle the situation itself. > + * We need to avoid as much as possible querying the running KVM type > + * in QEMU level. > + */ > +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu) > +{ > + CPUState *cs = CPU(cpu); > + > + if (cap_ppc_pvr_compat) { > + return false; > + } > + > + return !kvmppc_is_pr(cs->kvm_state); > +} > diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h > index 6bc6fb3..381afe6 100644 > --- a/target/ppc/kvm_ppc.h > +++ b/target/ppc/kvm_ppc.h > @@ -67,6 +67,7 @@ void kvmppc_check_papr_resize_hpt(Error **errp); > int kvmppc_resize_hpt_prepare(PowerPCCPU *cpu, target_ulong flags, int shift); > int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift); > void kvmppc_update_sdr1(target_ulong sdr1); > +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu); > > bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path); > > diff --git a/target/ppc/machine.c b/target/ppc/machine.c > index f578156..e545885 100644 > --- a/target/ppc/machine.c > +++ b/target/ppc/machine.c > @@ -9,6 +9,7 @@ > #include "mmu-hash64.h" > #include "migration/cpu.h" > #include "qapi/error.h" > +#include "kvm_ppc.h" > > static int cpu_load_old(QEMUFile *f, void *opaque, int version_id) > { > @@ -250,6 +251,27 @@ static int cpu_post_load(void *opaque, int version_id) > } > } > > + /* > + * If we're running with KVM HV, there is a chance that the guest > + * is running with KVM HV and its kernel does not have the > + * capability of dealing with a different PVR other than this > + * exact host PVR in KVM_SET_SREGS. If that happens, the > + * guest freezes after migration. > + * > + * The function kvmppc_pvr_workaround_required does this verification > + * by first checking if the kernel has the cap, returning true immediately > + * if that is the case. Otherwise, it checks if we're running in KVM PR. > + * If the guest kernel does not have the cap and we're not running KVM-PR > + * (so, it is running KVM-HV), we need to ensure that KVM_SET_SREGS will > + * receive the PVR it expects as a workaround. > + * > + */ > +#if defined(CONFIG_KVM) > + if (kvmppc_pvr_workaround_required(cpu)) { > + env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value; > + } > +#endif > + > env->lr = env->spr[SPR_LR]; > env->ctr = env->spr[SPR_CTR]; > cpu_write_xer(env, env->spr[SPR_XER]);
On 08/09/2017 09:52 PM, David Gibson wrote: > On Wed, Aug 09, 2017 at 05:43:46PM -0300, Daniel Henrique Barboza wrote: >> 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> > Ugly, but necessary. Applied to ppc-for-2.10. Definitely not my finest hour either. Hopefully when we start looking at P8 -> P9 migrations we can clean this up or make it less ugly. Daniel > >> --- >> target/ppc/kvm.c | 34 ++++++++++++++++++++++++++++++++++ >> target/ppc/kvm_ppc.h | 1 + >> target/ppc/machine.c | 22 ++++++++++++++++++++++ >> 3 files changed, 57 insertions(+) >> >> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c >> index 8571379..fb3ee43 100644 >> --- a/target/ppc/kvm.c >> +++ b/target/ppc/kvm.c >> @@ -90,6 +90,7 @@ static int cap_htm; /* Hardware transactional memory support */ >> static int cap_mmu_radix; >> static int cap_mmu_hash_v3; >> static int cap_resize_hpt; >> +static int cap_ppc_pvr_compat; >> >> static uint32_t debug_inst_opcode; >> >> @@ -147,6 +148,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX); >> cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3); >> cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT); >> + /* >> + * Note: setting it to false because there is not such capability >> + * in KVM at this moment. >> + * >> + * TODO: call kvm_vm_check_extension() with the right capability >> + * after the kernel starts implementing it.*/ >> + cap_ppc_pvr_compat = false; >> >> if (!cap_interrupt_level) { >> fprintf(stderr, "KVM: Couldn't find level irq capability. Expect the " >> @@ -2785,3 +2793,29 @@ void kvmppc_update_sdr1(target_ulong sdr1) >> run_on_cpu(cs, kvmppc_pivot_hpt_cpu, RUN_ON_CPU_TARGET_PTR(sdr1)); >> } >> } >> + >> +/* >> + * This is a helper function to detect a post migration scenario >> + * in which a guest, running as KVM-HV, freezes in cpu_post_load because >> + * the guest kernel can't handle a PVR value other than the actual host >> + * PVR in KVM_SET_SREGS, even if pvr_match() returns true. >> + * >> + * If we don't have cap_ppc_pvr_compat and we're not running in PR >> + * (so, we're HV), return true. The workaround itself is done in >> + * cpu_post_load. >> + * >> + * The order here is important: we'll only check for KVM PR as a >> + * fallback if the guest kernel can't handle the situation itself. >> + * We need to avoid as much as possible querying the running KVM type >> + * in QEMU level. >> + */ >> +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu) >> +{ >> + CPUState *cs = CPU(cpu); >> + >> + if (cap_ppc_pvr_compat) { >> + return false; >> + } >> + >> + return !kvmppc_is_pr(cs->kvm_state); >> +} >> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h >> index 6bc6fb3..381afe6 100644 >> --- a/target/ppc/kvm_ppc.h >> +++ b/target/ppc/kvm_ppc.h >> @@ -67,6 +67,7 @@ void kvmppc_check_papr_resize_hpt(Error **errp); >> int kvmppc_resize_hpt_prepare(PowerPCCPU *cpu, target_ulong flags, int shift); >> int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift); >> void kvmppc_update_sdr1(target_ulong sdr1); >> +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu); >> >> bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path); >> >> diff --git a/target/ppc/machine.c b/target/ppc/machine.c >> index f578156..e545885 100644 >> --- a/target/ppc/machine.c >> +++ b/target/ppc/machine.c >> @@ -9,6 +9,7 @@ >> #include "mmu-hash64.h" >> #include "migration/cpu.h" >> #include "qapi/error.h" >> +#include "kvm_ppc.h" >> >> static int cpu_load_old(QEMUFile *f, void *opaque, int version_id) >> { >> @@ -250,6 +251,27 @@ static int cpu_post_load(void *opaque, int version_id) >> } >> } >> >> + /* >> + * If we're running with KVM HV, there is a chance that the guest >> + * is running with KVM HV and its kernel does not have the >> + * capability of dealing with a different PVR other than this >> + * exact host PVR in KVM_SET_SREGS. If that happens, the >> + * guest freezes after migration. >> + * >> + * The function kvmppc_pvr_workaround_required does this verification >> + * by first checking if the kernel has the cap, returning true immediately >> + * if that is the case. Otherwise, it checks if we're running in KVM PR. >> + * If the guest kernel does not have the cap and we're not running KVM-PR >> + * (so, it is running KVM-HV), we need to ensure that KVM_SET_SREGS will >> + * receive the PVR it expects as a workaround. >> + * >> + */ >> +#if defined(CONFIG_KVM) >> + if (kvmppc_pvr_workaround_required(cpu)) { >> + env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value; >> + } >> +#endif >> + >> env->lr = env->spr[SPR_LR]; >> env->ctr = env->spr[SPR_CTR]; >> cpu_write_xer(env, env->spr[SPR_XER]);
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c index 8571379..fb3ee43 100644 --- a/target/ppc/kvm.c +++ b/target/ppc/kvm.c @@ -90,6 +90,7 @@ static int cap_htm; /* Hardware transactional memory support */ static int cap_mmu_radix; static int cap_mmu_hash_v3; static int cap_resize_hpt; +static int cap_ppc_pvr_compat; static uint32_t debug_inst_opcode; @@ -147,6 +148,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s) cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX); cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3); cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT); + /* + * Note: setting it to false because there is not such capability + * in KVM at this moment. + * + * TODO: call kvm_vm_check_extension() with the right capability + * after the kernel starts implementing it.*/ + cap_ppc_pvr_compat = false; if (!cap_interrupt_level) { fprintf(stderr, "KVM: Couldn't find level irq capability. Expect the " @@ -2785,3 +2793,29 @@ void kvmppc_update_sdr1(target_ulong sdr1) run_on_cpu(cs, kvmppc_pivot_hpt_cpu, RUN_ON_CPU_TARGET_PTR(sdr1)); } } + +/* + * This is a helper function to detect a post migration scenario + * in which a guest, running as KVM-HV, freezes in cpu_post_load because + * the guest kernel can't handle a PVR value other than the actual host + * PVR in KVM_SET_SREGS, even if pvr_match() returns true. + * + * If we don't have cap_ppc_pvr_compat and we're not running in PR + * (so, we're HV), return true. The workaround itself is done in + * cpu_post_load. + * + * The order here is important: we'll only check for KVM PR as a + * fallback if the guest kernel can't handle the situation itself. + * We need to avoid as much as possible querying the running KVM type + * in QEMU level. + */ +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu) +{ + CPUState *cs = CPU(cpu); + + if (cap_ppc_pvr_compat) { + return false; + } + + return !kvmppc_is_pr(cs->kvm_state); +} diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h index 6bc6fb3..381afe6 100644 --- a/target/ppc/kvm_ppc.h +++ b/target/ppc/kvm_ppc.h @@ -67,6 +67,7 @@ void kvmppc_check_papr_resize_hpt(Error **errp); int kvmppc_resize_hpt_prepare(PowerPCCPU *cpu, target_ulong flags, int shift); int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift); void kvmppc_update_sdr1(target_ulong sdr1); +bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu); bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path); diff --git a/target/ppc/machine.c b/target/ppc/machine.c index f578156..e545885 100644 --- a/target/ppc/machine.c +++ b/target/ppc/machine.c @@ -9,6 +9,7 @@ #include "mmu-hash64.h" #include "migration/cpu.h" #include "qapi/error.h" +#include "kvm_ppc.h" static int cpu_load_old(QEMUFile *f, void *opaque, int version_id) { @@ -250,6 +251,27 @@ static int cpu_post_load(void *opaque, int version_id) } } + /* + * If we're running with KVM HV, there is a chance that the guest + * is running with KVM HV and its kernel does not have the + * capability of dealing with a different PVR other than this + * exact host PVR in KVM_SET_SREGS. If that happens, the + * guest freezes after migration. + * + * The function kvmppc_pvr_workaround_required does this verification + * by first checking if the kernel has the cap, returning true immediately + * if that is the case. Otherwise, it checks if we're running in KVM PR. + * If the guest kernel does not have the cap and we're not running KVM-PR + * (so, it is running KVM-HV), we need to ensure that KVM_SET_SREGS will + * receive the PVR it expects as a workaround. + * + */ +#if defined(CONFIG_KVM) + if (kvmppc_pvr_workaround_required(cpu)) { + env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value; + } +#endif + env->lr = env->spr[SPR_LR]; env->ctr = env->spr[SPR_CTR]; cpu_write_xer(env, env->spr[SPR_XER]);
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> --- target/ppc/kvm.c | 34 ++++++++++++++++++++++++++++++++++ target/ppc/kvm_ppc.h | 1 + target/ppc/machine.c | 22 ++++++++++++++++++++++ 3 files changed, 57 insertions(+)