From: Nicholas Piggin <npiggin@gmail.com> To: kvm-ppc@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin <npiggin@gmail.com> Subject: [PATCH v7 22/32] KVM: PPC: Book3S HV: Remove support for dependent threads mode on P9 Date: Fri, 28 May 2021 19:07:42 +1000 [thread overview] Message-ID: <20210528090752.3542186-23-npiggin@gmail.com> (raw) In-Reply-To: <20210528090752.3542186-1-npiggin@gmail.com> Dependent-threads mode is the normal KVM mode for pre-POWER9 SMT processors, where all threads in a core (or subcore) would run the same partition at the same time, or they would run the host. This design was mandated by MMU state that is shared between threads in a processor, so the synchronisation point is in hypervisor real-mode that has essentially no shared state, so it's safe for multiple threads to gather and switch to the correct mode. It is implemented by having the host unplug all secondary threads and always run in SMT1 mode, and host QEMU threads essentially represent virtual cores that wake these secondary threads out of unplug when the ioctl is called to run the guest. This happens via a side-path that is mostly invisible to the rest of the Linux host and the secondary threads still appear to be unplugged. POWER9 / ISA v3.0 has a more flexible MMU design that is independent per-thread and allows a much simpler KVM implementation. Before the new "P9 fast path" was added that began to take advantage of this, POWER9 support was implemented in the existing path which has support to run in the dependent threads mode. So it was not much work to add support to run POWER9 in this dependent threads mode. The mode is not required by the POWER9 MMU (although "mixed-mode" hash / radix MMU limitations of early processors were worked around using this mode). But it is one way to run SMT guests without running different guests or guest and host on different threads of the same core, so it could avoid or reduce some SMT attack surfaces without turning off SMT entirely. This security feature has some real, if indeterminate, value. However the old path is lagging in features (nested HV), and with this series the new P9 path adds remaining missing features (radix prefetch bug and hash support, in later patches), so POWER9 dependent threads mode support would be the only remaining reason to keep that code in and keep supporting POWER9/POWER10 in the old path. So here we make the call to drop this feature. Remove dependent threads mode support for POWER9 and above processors. Systems can still achieve this security by disabling SMT entirely, but that would generally come at a larger performance cost for guests. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/include/asm/kvm_asm.h | 2 +- arch/powerpc/include/asm/kvm_host.h | 1 - arch/powerpc/kvm/book3s_64_entry.S | 3 +-- arch/powerpc/kvm/book3s_hv.c | 27 +++++---------------------- 4 files changed, 7 insertions(+), 26 deletions(-) diff --git a/arch/powerpc/include/asm/kvm_asm.h b/arch/powerpc/include/asm/kvm_asm.h index 43b1788e1f93..f4ae37810aa9 100644 --- a/arch/powerpc/include/asm/kvm_asm.h +++ b/arch/powerpc/include/asm/kvm_asm.h @@ -147,7 +147,7 @@ #define KVM_GUEST_MODE_SKIP 2 #define KVM_GUEST_MODE_GUEST_HV 3 #define KVM_GUEST_MODE_HOST_HV 4 -#define KVM_GUEST_MODE_HV_FAST 5 /* ISA >= v3.0 host+guest radix, indep thr */ +#define KVM_GUEST_MODE_HV_FAST 5 /* ISA >= v3.0 host+guest radix */ #define KVM_INST_FETCH_FAILED -1 diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 69add9d662df..6904ce9e8190 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -297,7 +297,6 @@ struct kvm_arch { u8 fwnmi_enabled; u8 secure_guest; u8 svm_enabled; - bool threads_indep; bool nested_enable; bool dawr1_enabled; pgd_t *pgtable; diff --git a/arch/powerpc/kvm/book3s_64_entry.S b/arch/powerpc/kvm/book3s_64_entry.S index 177e8fad5c8d..bac664c1a9f7 100644 --- a/arch/powerpc/kvm/book3s_64_entry.S +++ b/arch/powerpc/kvm/book3s_64_entry.S @@ -184,8 +184,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) * void kvmppc_p9_enter_guest(struct vcpu *vcpu); * * Enter the guest on a ISAv3.0 or later system where we have exactly - * one vcpu per vcore, and both the host and guest are radix, and threads - * are set to "indepdent mode". + * one vcpu per vcore, and both the host and guest are radix. */ .balign IFETCH_ALIGN_BYTES _GLOBAL(kvmppc_p9_enter_guest) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index eb25605e23b9..acb0c72ea900 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -103,13 +103,9 @@ static int target_smt_mode; module_param(target_smt_mode, int, 0644); MODULE_PARM_DESC(target_smt_mode, "Target threads per core (0 = max)"); -static bool indep_threads_mode = true; -module_param(indep_threads_mode, bool, S_IRUGO | S_IWUSR); -MODULE_PARM_DESC(indep_threads_mode, "Independent-threads mode (only on POWER9)"); - static bool one_vm_per_core; module_param(one_vm_per_core, bool, S_IRUGO | S_IWUSR); -MODULE_PARM_DESC(one_vm_per_core, "Only run vCPUs from the same VM on a core (requires indep_threads_mode=N)"); +MODULE_PARM_DESC(one_vm_per_core, "Only run vCPUs from the same VM on a core (requires POWER8 or older)"); #ifdef CONFIG_KVM_XICS static const struct kernel_param_ops module_param_ops = { @@ -2265,7 +2261,7 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id, */ static int threads_per_vcore(struct kvm *kvm) { - if (kvm->arch.threads_indep) + if (cpu_has_feature(CPU_FTR_ARCH_300)) return 1; return threads_per_subcore; } @@ -4369,7 +4365,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu) vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; do { - if (kvm->arch.threads_indep && kvm_is_radix(kvm)) + if (kvm_is_radix(kvm)) r = kvmhv_run_single_vcpu(vcpu, ~(u64)0, vcpu->arch.vcore->lpcr); else @@ -4992,21 +4988,8 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm) /* * Track that we now have a HV mode VM active. This blocks secondary * CPU threads from coming online. - * On POWER9, we only need to do this if the "indep_threads_mode" - * module parameter has been set to N. */ - if (cpu_has_feature(CPU_FTR_ARCH_300)) { - if (!indep_threads_mode && !cpu_has_feature(CPU_FTR_HVMODE)) { - pr_warn("KVM: Ignoring indep_threads_mode=N in nested hypervisor\n"); - kvm->arch.threads_indep = true; - } else if (!indep_threads_mode && cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) { - pr_warn("KVM: Ignoring indep_threads_mode=N on pre-DD2.2 POWER9\n"); - kvm->arch.threads_indep = true; - } else { - kvm->arch.threads_indep = indep_threads_mode; - } - } - if (!kvm->arch.threads_indep) + if (!cpu_has_feature(CPU_FTR_ARCH_300)) kvm_hv_vm_activated(); /* @@ -5047,7 +5030,7 @@ static void kvmppc_core_destroy_vm_hv(struct kvm *kvm) { debugfs_remove_recursive(kvm->arch.debugfs_dir); - if (!kvm->arch.threads_indep) + if (!cpu_has_feature(CPU_FTR_ARCH_300)) kvm_hv_vm_deactivated(); kvmppc_free_vcores(kvm); -- 2.23.0
WARNING: multiple messages have this Message-ID (diff)
From: Nicholas Piggin <npiggin@gmail.com> To: kvm-ppc@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin <npiggin@gmail.com> Subject: [PATCH v7 22/32] KVM: PPC: Book3S HV: Remove support for dependent threads mode on P9 Date: Fri, 28 May 2021 09:07:42 +0000 [thread overview] Message-ID: <20210528090752.3542186-23-npiggin@gmail.com> (raw) In-Reply-To: <20210528090752.3542186-1-npiggin@gmail.com> Dependent-threads mode is the normal KVM mode for pre-POWER9 SMT processors, where all threads in a core (or subcore) would run the same partition at the same time, or they would run the host. This design was mandated by MMU state that is shared between threads in a processor, so the synchronisation point is in hypervisor real-mode that has essentially no shared state, so it's safe for multiple threads to gather and switch to the correct mode. It is implemented by having the host unplug all secondary threads and always run in SMT1 mode, and host QEMU threads essentially represent virtual cores that wake these secondary threads out of unplug when the ioctl is called to run the guest. This happens via a side-path that is mostly invisible to the rest of the Linux host and the secondary threads still appear to be unplugged. POWER9 / ISA v3.0 has a more flexible MMU design that is independent per-thread and allows a much simpler KVM implementation. Before the new "P9 fast path" was added that began to take advantage of this, POWER9 support was implemented in the existing path which has support to run in the dependent threads mode. So it was not much work to add support to run POWER9 in this dependent threads mode. The mode is not required by the POWER9 MMU (although "mixed-mode" hash / radix MMU limitations of early processors were worked around using this mode). But it is one way to run SMT guests without running different guests or guest and host on different threads of the same core, so it could avoid or reduce some SMT attack surfaces without turning off SMT entirely. This security feature has some real, if indeterminate, value. However the old path is lagging in features (nested HV), and with this series the new P9 path adds remaining missing features (radix prefetch bug and hash support, in later patches), so POWER9 dependent threads mode support would be the only remaining reason to keep that code in and keep supporting POWER9/POWER10 in the old path. So here we make the call to drop this feature. Remove dependent threads mode support for POWER9 and above processors. Systems can still achieve this security by disabling SMT entirely, but that would generally come at a larger performance cost for guests. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/include/asm/kvm_asm.h | 2 +- arch/powerpc/include/asm/kvm_host.h | 1 - arch/powerpc/kvm/book3s_64_entry.S | 3 +-- arch/powerpc/kvm/book3s_hv.c | 27 +++++---------------------- 4 files changed, 7 insertions(+), 26 deletions(-) diff --git a/arch/powerpc/include/asm/kvm_asm.h b/arch/powerpc/include/asm/kvm_asm.h index 43b1788e1f93..f4ae37810aa9 100644 --- a/arch/powerpc/include/asm/kvm_asm.h +++ b/arch/powerpc/include/asm/kvm_asm.h @@ -147,7 +147,7 @@ #define KVM_GUEST_MODE_SKIP 2 #define KVM_GUEST_MODE_GUEST_HV 3 #define KVM_GUEST_MODE_HOST_HV 4 -#define KVM_GUEST_MODE_HV_FAST 5 /* ISA >= v3.0 host+guest radix, indep thr */ +#define KVM_GUEST_MODE_HV_FAST 5 /* ISA >= v3.0 host+guest radix */ #define KVM_INST_FETCH_FAILED -1 diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 69add9d662df..6904ce9e8190 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -297,7 +297,6 @@ struct kvm_arch { u8 fwnmi_enabled; u8 secure_guest; u8 svm_enabled; - bool threads_indep; bool nested_enable; bool dawr1_enabled; pgd_t *pgtable; diff --git a/arch/powerpc/kvm/book3s_64_entry.S b/arch/powerpc/kvm/book3s_64_entry.S index 177e8fad5c8d..bac664c1a9f7 100644 --- a/arch/powerpc/kvm/book3s_64_entry.S +++ b/arch/powerpc/kvm/book3s_64_entry.S @@ -184,8 +184,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) * void kvmppc_p9_enter_guest(struct vcpu *vcpu); * * Enter the guest on a ISAv3.0 or later system where we have exactly - * one vcpu per vcore, and both the host and guest are radix, and threads - * are set to "indepdent mode". + * one vcpu per vcore, and both the host and guest are radix. */ .balign IFETCH_ALIGN_BYTES _GLOBAL(kvmppc_p9_enter_guest) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index eb25605e23b9..acb0c72ea900 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -103,13 +103,9 @@ static int target_smt_mode; module_param(target_smt_mode, int, 0644); MODULE_PARM_DESC(target_smt_mode, "Target threads per core (0 = max)"); -static bool indep_threads_mode = true; -module_param(indep_threads_mode, bool, S_IRUGO | S_IWUSR); -MODULE_PARM_DESC(indep_threads_mode, "Independent-threads mode (only on POWER9)"); - static bool one_vm_per_core; module_param(one_vm_per_core, bool, S_IRUGO | S_IWUSR); -MODULE_PARM_DESC(one_vm_per_core, "Only run vCPUs from the same VM on a core (requires indep_threads_mode=N)"); +MODULE_PARM_DESC(one_vm_per_core, "Only run vCPUs from the same VM on a core (requires POWER8 or older)"); #ifdef CONFIG_KVM_XICS static const struct kernel_param_ops module_param_ops = { @@ -2265,7 +2261,7 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id, */ static int threads_per_vcore(struct kvm *kvm) { - if (kvm->arch.threads_indep) + if (cpu_has_feature(CPU_FTR_ARCH_300)) return 1; return threads_per_subcore; } @@ -4369,7 +4365,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu) vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; do { - if (kvm->arch.threads_indep && kvm_is_radix(kvm)) + if (kvm_is_radix(kvm)) r = kvmhv_run_single_vcpu(vcpu, ~(u64)0, vcpu->arch.vcore->lpcr); else @@ -4992,21 +4988,8 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm) /* * Track that we now have a HV mode VM active. This blocks secondary * CPU threads from coming online. - * On POWER9, we only need to do this if the "indep_threads_mode" - * module parameter has been set to N. */ - if (cpu_has_feature(CPU_FTR_ARCH_300)) { - if (!indep_threads_mode && !cpu_has_feature(CPU_FTR_HVMODE)) { - pr_warn("KVM: Ignoring indep_threads_mode=N in nested hypervisor\n"); - kvm->arch.threads_indep = true; - } else if (!indep_threads_mode && cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) { - pr_warn("KVM: Ignoring indep_threads_mode=N on pre-DD2.2 POWER9\n"); - kvm->arch.threads_indep = true; - } else { - kvm->arch.threads_indep = indep_threads_mode; - } - } - if (!kvm->arch.threads_indep) + if (!cpu_has_feature(CPU_FTR_ARCH_300)) kvm_hv_vm_activated(); /* @@ -5047,7 +5030,7 @@ static void kvmppc_core_destroy_vm_hv(struct kvm *kvm) { debugfs_remove_recursive(kvm->arch.debugfs_dir); - if (!kvm->arch.threads_indep) + if (!cpu_has_feature(CPU_FTR_ARCH_300)) kvm_hv_vm_deactivated(); kvmppc_free_vcores(kvm); -- 2.23.0
next prev parent reply other threads:[~2021-05-28 9:18 UTC|newest] Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-28 9:07 [PATCH v7 00/32] KVM: PPC: Book3S: C-ify the P9 entry/exit code Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 01/32] KVM: PPC: Book3S 64: move KVM interrupt entry to a common entry point Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-06-06 12:27 ` Michael Ellerman 2021-06-06 12:27 ` Michael Ellerman 2021-05-28 9:07 ` [PATCH v7 02/32] KVM: PPC: Book3S 64: Move GUEST_MODE_SKIP test into KVM Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 03/32] KVM: PPC: Book3S 64: add hcall interrupt handler Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 04/32] KVM: PPC: Book3S 64: Move hcall early register setup to KVM Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 05/32] KVM: PPC: Book3S 64: Move interrupt " Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 06/32] KVM: PPC: Book3S 64: move bad_host_intr check to HV handler Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 07/32] KVM: PPC: Book3S 64: Minimise hcall handler calling convention differences Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 08/32] KVM: PPC: Book3S HV P9: implement kvmppc_xive_pull_vcpu in C Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 09/32] KVM: PPC: Book3S HV P9: Move setting HDEC after switching to guest LPCR Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 10/32] KVM: PPC: Book3S HV P9: Reduce irq_work vs guest decrementer races Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 11/32] KVM: PPC: Book3S HV P9: Move xive vcpu context management into kvmhv_p9_guest_entry Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 12/32] KVM: PPC: Book3S HV P9: Move radix MMU switching instructions together Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 13/32] KVM: PPC: Book3S HV P9: Stop handling hcalls in real-mode in the P9 path Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 14/32] KVM: PPC: Book3S HV P9: Implement the rest of the P9 path in C Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 15/32] KVM: PPC: Book3S HV P9: inline kvmhv_load_hv_regs_and_go into __kvmhv_vcpu_entry_p9 Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 16/32] KVM: PPC: Book3S HV P9: Read machine check registers while MSR[RI] is 0 Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 17/32] KVM: PPC: Book3S HV P9: Improve exit timing accounting coverage Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 18/32] KVM: PPC: Book3S HV P9: Move SPR loading after expiry time check Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 19/32] KVM: PPC: Book3S HV P9: Add helpers for OS SPR handling Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 20/32] KVM: PPC: Book3S HV P9: Switch to guest MMU context as late as possible Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 21/32] KVM: PPC: Book3S HV: Implement radix prefetch workaround by disabling MMU Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin [this message] 2021-05-28 9:07 ` [PATCH v7 22/32] KVM: PPC: Book3S HV: Remove support for dependent threads mode on P9 Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 23/32] KVM: PPC: Book3S HV: Remove radix guest support from P7/8 path Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 24/32] KVM: PPC: Book3S HV: Remove virt mode checks from real mode handlers Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 25/32] KVM: PPC: Book3S HV: Remove unused nested HV tests in XICS emulation Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 26/32] KVM: PPC: Book3S HV P9: Allow all P9 processors to enable nested HV Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 27/32] KVM: PPC: Book3S HV: small pseries_do_hcall cleanup Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 28/32] KVM: PPC: Book3S HV: add virtual mode handlers for HPT hcalls and page faults Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 29/32] KVM: PPC: Book3S HV P9: Reflect userspace hcalls to hash guests to support PR KVM Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 30/32] KVM: PPC: Book3S HV P9: implement hash guest support Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 31/32] KVM: PPC: Book3S HV P9: implement hash host / " Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-05-28 9:07 ` [PATCH v7 32/32] KVM: PPC: Book3S HV: remove ISA v3.0 and v3.1 support from P7/8 path Nicholas Piggin 2021-05-28 9:07 ` Nicholas Piggin 2021-06-24 13:59 ` [PATCH v7 00/32] KVM: PPC: Book3S: C-ify the P9 entry/exit code Michael Ellerman 2021-06-24 13:59 ` Michael Ellerman -- strict thread matches above, loose matches on Subject: below -- 2021-05-28 9:06 Nicholas Piggin 2021-05-28 9:06 ` Nicholas Piggin
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