From 9dc2babc185e0a24fbb48098daafd552cac157fa Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Fri, 28 May 2021 19:07:33 +1000 Subject: KVM: PPC: Book3S HV P9: Stop handling hcalls in real-mode in the P9 path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In the interest of minimising the amount of code that is run in "real-mode", don't handle hcalls in real mode in the P9 path. This requires some new handlers for H_CEDE and xics-on-xive to be added before xive is pulled or cede logic is checked. This introduces a change in radix guest behaviour where radix guests that execute 'sc 1' in userspace now get a privilege fault whereas previously the 'sc 1' would be reflected as a syscall interrupt to the guest kernel. That reflection is only required for hash guests that run PR KVM. Background: In POWER8 and earlier processors, it is very expensive to exit from the HV real mode context of a guest hypervisor interrupt, and switch to host virtual mode. On those processors, guest->HV interrupts reach the hypervisor with the MMU off because the MMU is loaded with guest context (LPCR, SDR1, SLB), and the other threads in the sub-core need to be pulled out of the guest too. Then the primary must save off guest state, invalidate SLB and ERAT, and load up host state before the MMU can be enabled to run in host virtual mode (~= regular Linux mode). Hash guests also require a lot of hcalls to run due to the nature of the MMU architecture and paravirtualisation design. The XICS interrupt controller requires hcalls to run. So KVM traditionally tries hard to avoid the full exit, by handling hcalls and other interrupts in real mode as much as possible. By contrast, POWER9 has independent MMU context per-thread, and in radix mode the hypervisor is in host virtual memory mode when the HV interrupt is taken. Radix guests do not require significant hcalls to manage their translations, and xive guests don't need hcalls to handle interrupts. So it's much less important for performance to handle hcalls in real mode on POWER9. One caveat is that the TCE hcalls are performance critical, real-mode variants introduced for POWER8 in order to achieve 10GbE performance. Real mode TCE hcalls were found to be less important on POWER9, which was able to drive 40GBe networking without them (using the virt mode hcalls) but performance is still important. These hcalls will benefit from subsequent guest entry/exit optimisation including possibly a faster "partial exit" that does not entirely switch to host context to handle the hcall. Signed-off-by: Nicholas Piggin Reviewed-by: Alexey Kardashevskiy Reviewed-by: Cédric Le Goater Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210528090752.3542186-14-npiggin@gmail.com --- arch/powerpc/kvm/book3s.c | 6 +++ arch/powerpc/kvm/book3s_hv.c | 79 ++++++++++++++++++++++++++++----- arch/powerpc/kvm/book3s_hv_rmhandlers.S | 5 +++ arch/powerpc/kvm/book3s_xive.c | 64 ++++++++++++++++++++++++++ 4 files changed, 143 insertions(+), 11 deletions(-) (limited to 'arch/powerpc/kvm') diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c index 2b691f4d1f26..d69560d5bf16 100644 --- a/arch/powerpc/kvm/book3s.c +++ b/arch/powerpc/kvm/book3s.c @@ -171,6 +171,12 @@ void kvmppc_core_queue_machine_check(struct kvm_vcpu *vcpu, ulong flags) } EXPORT_SYMBOL_GPL(kvmppc_core_queue_machine_check); +void kvmppc_core_queue_syscall(struct kvm_vcpu *vcpu) +{ + kvmppc_inject_interrupt(vcpu, BOOK3S_INTERRUPT_SYSCALL, 0); +} +EXPORT_SYMBOL(kvmppc_core_queue_syscall); + void kvmppc_core_queue_program(struct kvm_vcpu *vcpu, ulong flags) { /* might as well deliver this straight away */ diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 3ec1dc1bad16..8df02be9be72 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -899,6 +899,10 @@ static int kvm_arch_vcpu_yield_to(struct kvm_vcpu *target) * H_SUCCESS if the source vcore wasn't idle (e.g. if it may * have useful work to do and should not confer) so we don't * recheck that here. + * + * In the case of the P9 single vcpu per vcore case, the real + * mode handler is not called but no other threads are in the + * source vcore. */ spin_lock(&vcore->lock); @@ -1142,12 +1146,13 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu) } /* - * Handle H_CEDE in the nested virtualization case where we haven't - * called the real-mode hcall handlers in book3s_hv_rmhandlers.S. + * Handle H_CEDE in the P9 path where we don't call the real-mode hcall + * handlers in book3s_hv_rmhandlers.S. + * * This has to be done early, not in kvmppc_pseries_do_hcall(), so * that the cede logic in kvmppc_run_single_vcpu() works properly. */ -static void kvmppc_nested_cede(struct kvm_vcpu *vcpu) +static void kvmppc_cede(struct kvm_vcpu *vcpu) { vcpu->arch.shregs.msr |= MSR_EE; vcpu->arch.ceded = 1; @@ -1400,13 +1405,29 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu, } case BOOK3S_INTERRUPT_SYSCALL: { - /* hcall - punt to userspace */ int i; - /* hypercall with MSR_PR has already been handled in rmode, - * and never reaches here. - */ + if (unlikely(vcpu->arch.shregs.msr & MSR_PR)) { + /* + * Guest userspace executed sc 1. This can only be + * reached by the P9 path because the old path + * handles this case in realmode hcall handlers. + * + * Radix guests can not run PR KVM or nested HV hash + * guests which might run PR KVM, so this is always + * a privilege fault. Send a program check to guest + * kernel. + */ + kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV); + r = RESUME_GUEST; + break; + } + /* + * hcall - gather args and set exit_reason. This will next be + * handled by kvmppc_pseries_do_hcall which may be able to deal + * with it and resume guest, or may punt to userspace. + */ run->papr_hcall.nr = kvmppc_get_gpr(vcpu, 3); for (i = 0; i < 9; ++i) run->papr_hcall.args[i] = kvmppc_get_gpr(vcpu, 4 + i); @@ -3664,6 +3685,12 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit, return trap; } +static inline bool hcall_is_xics(unsigned long req) +{ + return req == H_EOI || req == H_CPPR || req == H_IPI || + req == H_IPOLL || req == H_XIRR || req == H_XIRR_X; +} + /* * Virtual-mode guest entry for POWER9 and later when the host and * guest are both using the radix MMU. The LPIDR has already been set. @@ -3787,15 +3814,36 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, /* H_CEDE has to be handled now, not later */ if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested && kvmppc_get_gpr(vcpu, 3) == H_CEDE) { - kvmppc_nested_cede(vcpu); + kvmppc_cede(vcpu); kvmppc_set_gpr(vcpu, 3, 0); trap = 0; } } else { kvmppc_xive_push_vcpu(vcpu); trap = kvmhv_load_hv_regs_and_go(vcpu, time_limit, lpcr); + if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested && + !(vcpu->arch.shregs.msr & MSR_PR)) { + unsigned long req = kvmppc_get_gpr(vcpu, 3); + + /* H_CEDE has to be handled now, not later */ + if (req == H_CEDE) { + kvmppc_cede(vcpu); + kvmppc_xive_rearm_escalation(vcpu); /* may un-cede */ + kvmppc_set_gpr(vcpu, 3, 0); + trap = 0; + + /* XICS hcalls must be handled before xive is pulled */ + } else if (hcall_is_xics(req)) { + int ret; + + ret = kvmppc_xive_xics_hcall(vcpu, req); + if (ret != H_TOO_HARD) { + kvmppc_set_gpr(vcpu, 3, ret); + trap = 0; + } + } + } kvmppc_xive_pull_vcpu(vcpu); - } vcpu->arch.slb_max = 0; @@ -4461,8 +4509,17 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu) else r = kvmppc_run_vcpu(vcpu); - if (run->exit_reason == KVM_EXIT_PAPR_HCALL && - !(vcpu->arch.shregs.msr & MSR_PR)) { + if (run->exit_reason == KVM_EXIT_PAPR_HCALL) { + if (WARN_ON_ONCE(vcpu->arch.shregs.msr & MSR_PR)) { + /* + * These should have been caught reflected + * into the guest by now. Final sanity check: + * don't allow userspace to execute hcalls in + * the hypervisor. + */ + r = RESUME_GUEST; + continue; + } trace_kvm_hcall_enter(vcpu); r = kvmppc_pseries_do_hcall(vcpu); trace_kvm_hcall_exit(vcpu, r); diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S index 55d4d5495f5d..0637126be21e 100644 --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S @@ -1400,9 +1400,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) mr r4,r9 bge fast_guest_return 2: + /* If we came in through the P9 short path, no real mode hcalls */ + lwz r0, STACK_SLOT_SHORT_PATH(r1) + cmpwi r0, 0 + bne no_try_real /* See if this is an hcall we can handle in real mode */ cmpwi r12,BOOK3S_INTERRUPT_SYSCALL beq hcall_try_real_mode +no_try_real: /* Hypervisor doorbell - exit only if host IPI flag set */ cmpwi r12, BOOK3S_INTERRUPT_H_DOORBELL diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c index 741bf1f4387a..24c07094651a 100644 --- a/arch/powerpc/kvm/book3s_xive.c +++ b/arch/powerpc/kvm/book3s_xive.c @@ -158,6 +158,40 @@ void kvmppc_xive_pull_vcpu(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvmppc_xive_pull_vcpu); +void kvmppc_xive_rearm_escalation(struct kvm_vcpu *vcpu) +{ + void __iomem *esc_vaddr = (void __iomem *)vcpu->arch.xive_esc_vaddr; + + if (!esc_vaddr) + return; + + /* we are using XIVE with single escalation */ + + if (vcpu->arch.xive_esc_on) { + /* + * If we still have a pending escalation, abort the cede, + * and we must set PQ to 10 rather than 00 so that we don't + * potentially end up with two entries for the escalation + * interrupt in the XIVE interrupt queue. In that case + * we also don't want to set xive_esc_on to 1 here in + * case we race with xive_esc_irq(). + */ + vcpu->arch.ceded = 0; + /* + * The escalation interrupts are special as we don't EOI them. + * There is no need to use the load-after-store ordering offset + * to set PQ to 10 as we won't use StoreEOI. + */ + __raw_readq(esc_vaddr + XIVE_ESB_SET_PQ_10); + } else { + vcpu->arch.xive_esc_on = true; + mb(); + __raw_readq(esc_vaddr + XIVE_ESB_SET_PQ_00); + } + mb(); +} +EXPORT_SYMBOL_GPL(kvmppc_xive_rearm_escalation); + /* * This is a simple trigger for a generic XIVE IRQ. This must * only be called for interrupts that support a trigger page @@ -2106,6 +2140,36 @@ static int kvmppc_xive_create(struct kvm_device *dev, u32 type) return 0; } +int kvmppc_xive_xics_hcall(struct kvm_vcpu *vcpu, u32 req) +{ + struct kvmppc_vcore *vc = vcpu->arch.vcore; + + /* The VM should have configured XICS mode before doing XICS hcalls. */ + if (!kvmppc_xics_enabled(vcpu)) + return H_TOO_HARD; + + switch (req) { + case H_XIRR: + return xive_vm_h_xirr(vcpu); + case H_CPPR: + return xive_vm_h_cppr(vcpu, kvmppc_get_gpr(vcpu, 4)); + case H_EOI: + return xive_vm_h_eoi(vcpu, kvmppc_get_gpr(vcpu, 4)); + case H_IPI: + return xive_vm_h_ipi(vcpu, kvmppc_get_gpr(vcpu, 4), + kvmppc_get_gpr(vcpu, 5)); + case H_IPOLL: + return xive_vm_h_ipoll(vcpu, kvmppc_get_gpr(vcpu, 4)); + case H_XIRR_X: + xive_vm_h_xirr(vcpu); + kvmppc_set_gpr(vcpu, 5, get_tb() + vc->tb_offset); + return H_SUCCESS; + } + + return H_UNSUPPORTED; +} +EXPORT_SYMBOL_GPL(kvmppc_xive_xics_hcall); + int kvmppc_xive_debug_show_queues(struct seq_file *m, struct kvm_vcpu *vcpu) { struct kvmppc_xive_vcpu *xc = vcpu->arch.xive_vcpu; -- cgit v1.2.3