From 460df4c1fc7c00829050c08d6368dc6e6beef307 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 8 Feb 2017 11:50:15 +0100 Subject: [PATCH] KVM: race-free exit from KVM_RUN without POSIX signals MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The purpose of the KVM_SET_SIGNAL_MASK API is to let userspace "kick" a VCPU out of KVM_RUN through a POSIX signal. A signal is attached to a dummy signal handler; by blocking the signal outside KVM_RUN and unblocking it inside, this possible race is closed: VCPU thread service thread -------------------------------------------------------------- check flag set flag raise signal (signal handler does nothing) KVM_RUN However, one issue with KVM_SET_SIGNAL_MASK is that it has to take tsk->sighand->siglock on every KVM_RUN. This lock is often on a remote NUMA node, because it is on the node of a thread's creator. Taking this lock can be very expensive if there are many userspace exits (as is the case for SMP Windows VMs without Hyper-V reference time counter). As an alternative, we can put the flag directly in kvm_run so that KVM can see it: VCPU thread service thread -------------------------------------------------------------- raise signal signal handler set run->immediate_exit KVM_RUN check run->immediate_exit Reviewed-by: Radim Krčmář Reviewed-by: David Hildenbrand Signed-off-by: Paolo Bonzini --- Documentation/virtual/kvm/api.txt | 13 ++++++++++++- arch/arm/kvm/arm.c | 4 ++++ arch/mips/kvm/mips.c | 7 ++++++- arch/powerpc/kvm/powerpc.c | 6 +++++- arch/s390/kvm/kvm-s390.c | 4 ++++ arch/x86/kvm/x86.c | 6 +++++- include/uapi/linux/kvm.h | 4 +++- 7 files changed, 39 insertions(+), 5 deletions(-) diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index e4f2cdc..0694509 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3389,7 +3389,18 @@ struct kvm_run { Request that KVM_RUN return when it becomes possible to inject external interrupts into the guest. Useful in conjunction with KVM_INTERRUPT. - __u8 padding1[7]; + __u8 immediate_exit; + +This field is polled once when KVM_RUN starts; if non-zero, KVM_RUN +exits immediately, returning -EINTR. In the common scenario where a +signal is used to "kick" a VCPU out of KVM_RUN, this field can be used +to avoid usage of KVM_SET_SIGNAL_MASK, which has worse scalability. +Rather than blocking the signal outside KVM_RUN, userspace can set up +a signal handler that sets run->immediate_exit to a non-zero value. + +This field is ignored if KVM_CAP_IMMEDIATE_EXIT is not available. + + __u8 padding1[6]; /* out */ __u32 exit_reason; diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c index 21c493a..c9a2103 100644 --- a/arch/arm/kvm/arm.c +++ b/arch/arm/kvm/arm.c @@ -206,6 +206,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_ARM_PSCI_0_2: case KVM_CAP_READONLY_MEM: case KVM_CAP_MP_STATE: + case KVM_CAP_IMMEDIATE_EXIT: r = 1; break; case KVM_CAP_COALESCED_MMIO: @@ -604,6 +605,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) return ret; } + if (run->immediate_exit) + return -EINTR; + if (vcpu->sigset_active) sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved); diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c index 31ee5ee..ed81e5a 100644 --- a/arch/mips/kvm/mips.c +++ b/arch/mips/kvm/mips.c @@ -397,7 +397,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu, int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) { - int r = 0; + int r = -EINTR; sigset_t sigsaved; if (vcpu->sigset_active) @@ -409,6 +409,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) vcpu->mmio_needed = 0; } + if (run->immediate_exit) + goto out; + lose_fpu(1); local_irq_disable(); @@ -429,6 +432,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) guest_exit_irqoff(); local_irq_enable(); +out: if (vcpu->sigset_active) sigprocmask(SIG_SETMASK, &sigsaved, NULL); @@ -1021,6 +1025,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_ENABLE_CAP: case KVM_CAP_READONLY_MEM: case KVM_CAP_SYNC_MMU: + case KVM_CAP_IMMEDIATE_EXIT: r = 1; break; case KVM_CAP_COALESCED_MMIO: diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index 2b3e4e6..1fe1391 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -511,6 +511,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_ONE_REG: case KVM_CAP_IOEVENTFD: case KVM_CAP_DEVICE_CTRL: + case KVM_CAP_IMMEDIATE_EXIT: r = 1; break; case KVM_CAP_PPC_PAIRED_SINGLES: @@ -1117,7 +1118,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) #endif } - r = kvmppc_vcpu_run(run, vcpu); + if (run->immediate_exit) + r = -EINTR; + else + r = kvmppc_vcpu_run(run, vcpu); if (vcpu->sigset_active) sigprocmask(SIG_SETMASK, &sigsaved, NULL); diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 502de74..99e35fe 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -370,6 +370,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_S390_IRQCHIP: case KVM_CAP_VM_ATTRIBUTES: case KVM_CAP_MP_STATE: + case KVM_CAP_IMMEDIATE_EXIT: case KVM_CAP_S390_INJECT_IRQ: case KVM_CAP_S390_USER_SIGP: case KVM_CAP_S390_USER_STSI: @@ -2798,6 +2799,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) int rc; sigset_t sigsaved; + if (kvm_run->immediate_exit) + return -EINTR; + if (guestdbg_exit_pending(vcpu)) { kvm_s390_prepare_debug_exit(vcpu); return 0; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0aa8db2..8d3047c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2672,6 +2672,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_DISABLE_QUIRKS: case KVM_CAP_SET_BOOT_CPU_ID: case KVM_CAP_SPLIT_IRQCHIP: + case KVM_CAP_IMMEDIATE_EXIT: #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT case KVM_CAP_ASSIGN_DEV_IRQ: case KVM_CAP_PCI_2_3: @@ -7202,7 +7203,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) } else WARN_ON(vcpu->arch.pio.count || vcpu->mmio_needed); - r = vcpu_run(vcpu); + if (kvm_run->immediate_exit) + r = -EINTR; + else + r = vcpu_run(vcpu); out: post_kvm_run_save(vcpu); diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 7964b97..f51d508 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -218,7 +218,8 @@ struct kvm_hyperv_exit { struct kvm_run { /* in */ __u8 request_interrupt_window; - __u8 padding1[7]; + __u8 immediate_exit; + __u8 padding1[6]; /* out */ __u32 exit_reason; @@ -881,6 +882,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_SPAPR_RESIZE_HPT 133 #define KVM_CAP_PPC_MMU_RADIX 134 #define KVM_CAP_PPC_MMU_HASH_V3 135 +#define KVM_CAP_IMMEDIATE_EXIT 136 #ifdef KVM_CAP_IRQ_ROUTING -- 2.7.4