From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dfmNg-0005tn-6k for qemu-devel@nongnu.org; Thu, 10 Aug 2017 08:16:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dfmNc-0001ok-4A for qemu-devel@nongnu.org; Thu, 10 Aug 2017 08:16:04 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56715 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dfmNb-0001oL-UB for qemu-devel@nongnu.org; Thu, 10 Aug 2017 08:16:00 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v7ACE0I8135084 for ; Thu, 10 Aug 2017 08:15:59 -0400 Received: from e38.co.us.ibm.com (e38.co.us.ibm.com [32.97.110.159]) by mx0b-001b2d01.pphosted.com with ESMTP id 2c8m4a19fv-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 10 Aug 2017 08:15:58 -0400 Received: from localhost by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 10 Aug 2017 06:15:57 -0600 References: <20170809204346.5220-1-danielhb@linux.vnet.ibm.com> <20170810005256.GS13670@umbus.fritz.box> From: Daniel Henrique Barboza Date: Thu, 10 Aug 2017 09:15:47 -0300 MIME-Version: 1.0 In-Reply-To: <20170810005256.GS13670@umbus.fritz.box> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Message-Id: <2d973303-c75d-7ec8-51d7-2ffaae6d17dd@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH] target/ppc: 'PVR != host PVR' in KVM_SET_SREGS workaround List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com 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 > 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]);