From fbe4a7e881d4408bfabbb4fd538f10fd686cd8ab Mon Sep 17 00:00:00 2001 From: Yi Wang Date: Mon, 6 May 2024 18:17:49 +0800 Subject: [PATCH] KVM: Setup empty IRQ routing when creating a VM Setup empty IRQ routing during VM creation so that x86 and s390 don't need to set empty/dummy IRQ routing during KVM_CREATE_IRQCHIP (in future patches). Initializing IRQ routing before there are any potential readers allows KVM to avoid the synchronize_srcu() in kvm_set_irq_routing(), which can introduces 20+ milliseconds of latency in the VM creation path. Ensuring that all VMs have non-NULL IRQ routing also hardens KVM against misbehaving userspace VMMs, e.g. RISC-V dynamically instantiates its interrupt controller, but doesn't override kvm_arch_intc_initialized() or kvm_arch_irqfd_allowed(), and so can likely reach kvm_irq_map_gsi() without fully initialized IRQ routing. Signed-off-by: Yi Wang Acked-by: Christian Borntraeger Link: https://lore.kernel.org/r/20240506101751.3145407-2-foxywang@tencent.com [sean: init refcount after IRQ routing, fix stub, massage changelog] Signed-off-by: Sean Christopherson --- include/linux/kvm_host.h | 6 ++++++ virt/kvm/irqchip.c | 24 ++++++++++++++++++++++++ virt/kvm/kvm_main.c | 7 +++++++ 3 files changed, 37 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index c80fe03a1fa4..eaa70e9b1218 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2094,6 +2094,7 @@ int kvm_set_irq_routing(struct kvm *kvm, const struct kvm_irq_routing_entry *entries, unsigned nr, unsigned flags); +int kvm_init_irq_routing(struct kvm *kvm); int kvm_set_routing_entry(struct kvm *kvm, struct kvm_kernel_irq_routing_entry *e, const struct kvm_irq_routing_entry *ue); @@ -2103,6 +2104,11 @@ void kvm_free_irq_routing(struct kvm *kvm); static inline void kvm_free_irq_routing(struct kvm *kvm) {} +static inline int kvm_init_irq_routing(struct kvm *kvm) +{ + return 0; +} + #endif int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi); diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c index 1e567d1f6d3d..162d8ed889f2 100644 --- a/virt/kvm/irqchip.c +++ b/virt/kvm/irqchip.c @@ -237,3 +237,27 @@ out: return r; } + +/* + * Allocate empty IRQ routing by default so that additional setup isn't needed + * when userspace-driven IRQ routing is activated, and so that kvm->irq_routing + * is guaranteed to be non-NULL. + */ +int kvm_init_irq_routing(struct kvm *kvm) +{ + struct kvm_irq_routing_table *new; + int chip_size; + + new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT); + if (!new) + return -ENOMEM; + + new->nr_rt_entries = 1; + + chip_size = sizeof(int) * KVM_NR_IRQCHIPS * KVM_IRQCHIP_NUM_PINS; + memset(new->chip, -1, chip_size); + + RCU_INIT_POINTER(kvm->irq_routing, new); + + return 0; +} diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f4f5a435b225..7bf1ef0fc10b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1186,7 +1186,12 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) if (init_srcu_struct(&kvm->irq_srcu)) goto out_err_no_irq_srcu; + r = kvm_init_irq_routing(kvm); + if (r) + goto out_err_no_irq_routing; + refcount_set(&kvm->users_count, 1); + for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) { for (j = 0; j < 2; j++) { slots = &kvm->__memslots[i][j]; @@ -1265,6 +1270,8 @@ out_err_no_arch_destroy_vm: WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count)); for (i = 0; i < KVM_NR_BUSES; i++) kfree(kvm_get_bus(kvm, i)); + kvm_free_irq_routing(kvm); +out_err_no_irq_routing: cleanup_srcu_struct(&kvm->irq_srcu); out_err_no_irq_srcu: cleanup_srcu_struct(&kvm->srcu);