On Tue, 19 Nov 2019 at 20:11, Liran Alon <liran.alon@xxxxxxxxxx> wrote: > > > > > On 19 Nov 2019, at 8:36, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > > > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > > > ICR and TSCDEADLINE MSRs write cause the main MSRs write vmexits in > > our product observation, multicast IPIs are not as common as unicast > > IPI like RESCHEDULE_VECTOR and CALL_FUNCTION_SINGLE_VECTOR etc. > > > > This patch tries to optimize x2apic physical destination mode, fixed > > delivery mode single target IPI by delivering IPI to receiver as soon > > as possible after sender writes ICR vmexit to avoid various checks > > when possible, especially when running guest w/ --overcommit cpu-pm=on > > or guest can keep running, IPI can be injected to target vCPU by > > posted-interrupt immediately. > > > > Testing on Xeon Skylake server: > > > > The virtual IPI latency from sender send to receiver receive reduces > > more than 200+ cpu cycles. > > > > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > --- > > v1 -> v2: > > * add tracepoint > > * Instead of a separate vcpu->fast_vmexit, set exit_reason > > to vmx->exit_reason to -1 if the fast path succeeds. > > * move the "kvm_skip_emulated_instruction(vcpu)" to vmx_handle_exit > > * moving the handling into vmx_handle_exit_irqoff() > > > > arch/x86/include/asm/kvm_host.h | 4 ++-- > > arch/x86/include/uapi/asm/vmx.h | 1 + > > arch/x86/kvm/svm.c | 4 ++-- > > arch/x86/kvm/vmx/vmx.c | 40 +++++++++++++++++++++++++++++++++++++--- > > arch/x86/kvm/x86.c | 5 +++-- > > 5 files changed, 45 insertions(+), 9 deletions(-) > > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > index 898ab9e..0daafa9 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -1084,7 +1084,7 @@ struct kvm_x86_ops { > > void (*tlb_flush_gva)(struct kvm_vcpu *vcpu, gva_t addr); > > > > void (*run)(struct kvm_vcpu *vcpu); > > - int (*handle_exit)(struct kvm_vcpu *vcpu); > > + int (*handle_exit)(struct kvm_vcpu *vcpu, u32 *vcpu_exit_reason); > > int (*skip_emulated_instruction)(struct kvm_vcpu *vcpu); > > void (*set_interrupt_shadow)(struct kvm_vcpu *vcpu, int mask); > > u32 (*get_interrupt_shadow)(struct kvm_vcpu *vcpu); > > @@ -1134,7 +1134,7 @@ struct kvm_x86_ops { > > int (*check_intercept)(struct kvm_vcpu *vcpu, > > struct x86_instruction_info *info, > > enum x86_intercept_stage stage); > > - void (*handle_exit_irqoff)(struct kvm_vcpu *vcpu); > > + void (*handle_exit_irqoff)(struct kvm_vcpu *vcpu, u32 *vcpu_exit_reason); > > bool (*mpx_supported)(void); > > bool (*xsaves_supported)(void); > > bool (*umip_emulated)(void); > > diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h > > index 3eb8411..b33c6e1 100644 > > --- a/arch/x86/include/uapi/asm/vmx.h > > +++ b/arch/x86/include/uapi/asm/vmx.h > > @@ -88,6 +88,7 @@ > > #define EXIT_REASON_XRSTORS 64 > > #define EXIT_REASON_UMWAIT 67 > > #define EXIT_REASON_TPAUSE 68 > > +#define EXIT_REASON_NEED_SKIP_EMULATED_INSN -1 > > > > #define VMX_EXIT_REASONS \ > > { EXIT_REASON_EXCEPTION_NMI, "EXCEPTION_NMI" }, \ > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > > index d02a73a..c8e063a 100644 > > --- a/arch/x86/kvm/svm.c > > +++ b/arch/x86/kvm/svm.c > > @@ -4929,7 +4929,7 @@ static void svm_get_exit_info(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2) > > *info2 = control->exit_info_2; > > } > > > > -static int handle_exit(struct kvm_vcpu *vcpu) > > +static int handle_exit(struct kvm_vcpu *vcpu, u32 *vcpu_exit_reason) > > { > > struct vcpu_svm *svm = to_svm(vcpu); > > struct kvm_run *kvm_run = vcpu->run; > > @@ -6187,7 +6187,7 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu, > > return ret; > > } > > > > -static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu) > > +static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu, u32 *vcpu_exit_reason) > > { > > > > } > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index 621142e5..b98198d 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -5792,7 +5792,7 @@ void dump_vmcs(void) > > * The guest has exited. See if we can fix it or if we need userspace > > * assistance. > > */ > > -static int vmx_handle_exit(struct kvm_vcpu *vcpu) > > +static int vmx_handle_exit(struct kvm_vcpu *vcpu, u32 *vcpu_exit_reason) > > vmx_handle_exit() should get second parameter by value and not by pointer. As it doesn’t need to modify it. > > I would also rename parameter to “accel_exit_completion” to indicate this is additional work that needs to happen to complete accelerated-exit handling. > This parameter should be an enum that currently only have 2 values: ACCEL_EXIT_NONE and ACCEL_EXIT_SKIP_EMUL_INS. > > > { > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > u32 exit_reason = vmx->exit_reason; > > @@ -5878,7 +5878,10 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu) > > } > > } > > > > - if (exit_reason < kvm_vmx_max_exit_handlers > > + if (*vcpu_exit_reason == EXIT_REASON_NEED_SKIP_EMULATED_INSN) { > > + kvm_skip_emulated_instruction(vcpu); > > + return 1; > > + } else if (exit_reason < kvm_vmx_max_exit_handlers > > && kvm_vmx_exit_handlers[exit_reason]) { > > #ifdef CONFIG_RETPOLINE > > if (exit_reason == EXIT_REASON_MSR_WRITE) > > @@ -6223,7 +6226,36 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu) > > } > > STACK_FRAME_NON_STANDARD(handle_external_interrupt_irqoff); > > > > -static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu) > > +static u32 handle_ipi_fastpath(struct kvm_vcpu *vcpu) > > +{ > > + u32 index; > > + u64 data; > > + int ret = 0; > > + > > + if (lapic_in_kernel(vcpu) && apic_x2apic_mode(vcpu->arch.apic)) { > > + /* > > + * fastpath to IPI target, FIXED+PHYSICAL which is popular > > + */ > > + index = kvm_rcx_read(vcpu); > > + data = kvm_read_edx_eax(vcpu); > > + > > + if (((index - APIC_BASE_MSR) << 4 == APIC_ICR) && > > + ((data & KVM_APIC_DEST_MASK) == APIC_DEST_PHYSICAL) && > > + ((data & APIC_MODE_MASK) == APIC_DM_FIXED)) { > > + > > + trace_kvm_msr_write(index, data); > > On a standard EXIT_REASON_MSR_WRITE VMExit, this trace will be printed only after LAPIC emulation logic happens. > You should preserve same ordering. > > > + kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR2, (u32)(data >> 32)); > > + ret = kvm_lapic_reg_write(vcpu->arch.apic, APIC_ICR, (u32)data); > > + > > + if (ret == 0) > > + return EXIT_REASON_NEED_SKIP_EMULATED_INSN; > > + } > > + } > > + > > + return ret; > > +} > > Maybe it would be more elegant to modify this function as follows? > > static int handle_accel_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u32 msr, u64 data) > { > if (lapic_in_kernel(vcpu) && apic_x2apic_mode(vcpu->arch.apic) && > ((data & KVM_APIC_DEST_MASK) == APIC_DEST_PHYSICAL) && > ((data & APIC_MODE_MASK) == APIC_DM_FIXED)) { > > kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR2, (u32)(data >> 32)); > return kvm_lapic_reg_write(vcpu->arch.apic, APIC_ICR, (u32)data); > } > > return 1; > } > > static enum accel_exit_completion handle_accel_set_msr_irqoff(struct kvm_vcpu *vcpu) > { > u32 msr = kvm_rcx_read(vcpu); > u64 data = kvm_read_edx_eax(vcpu); > int ret = 0; > > switch (msr) { > case APIC_BASE_MSR + (APIC_ICR >> 4): > ret = handle_accel_set_x2apic_icr_irqoff(vcpu, msr, data); > break; > default: > return ACCEL_EXIT_NONE; > } > > if (!ret) { > trace_kvm_msr_write(msr, data); > return ACCEL_EXIT_SKIP_EMUL_INS; > } > > return ACCEL_EXIT_NONE; > } > > > + > > +static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu, u32 *exit_reason) > > { > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > > > @@ -6231,6 +6263,8 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu) > > handle_external_interrupt_irqoff(vcpu); > > else if (vmx->exit_reason == EXIT_REASON_EXCEPTION_NMI) > > handle_exception_nmi_irqoff(vmx); > > + else if (vmx->exit_reason == EXIT_REASON_MSR_WRITE) > > + *exit_reason = handle_ipi_fastpath(vcpu); > > 1) This case requires a comment as the only reason it is called here is an optimisation. > In contrast to the other cases which must be called before interrupts are enabled on the host. > > 2) I would rename handler to handle_accel_set_msr_irqoff(). > To signal this handler runs with host interrupts disabled and to make it a general place for accelerating WRMSRs in case we would require more in the future. Yes, TSCDEADLINE/VMX PREEMPTION TIMER is in my todo list after this merged upstream, handle all the comments in v3, thanks for making this nicer further. :) Wanpeng