From b321c31c9b7b309dcde5e8854b741c8e6a9a05f0 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 13 Jul 2023 08:06:57 +0100 Subject: [PATCH] KVM: arm64: vgic-v4: Make the doorbell request robust w.r.t preemption Xiang reports that VMs occasionally fail to boot on GICv4.1 systems when running a preemptible kernel, as it is possible that a vCPU is blocked without requesting a doorbell interrupt. The issue is that any preemption that occurs between vgic_v4_put() and schedule() on the block path will mark the vPE as nonresident and *not* request a doorbell irq. This occurs because when the vcpu thread is resumed on its way to block, vcpu_load() will make the vPE resident again. Once the vcpu actually blocks, we don't request a doorbell anymore, and the vcpu won't be woken up on interrupt delivery. Fix it by tracking that we're entering WFI, and key the doorbell request on that flag. This allows us not to make the vPE resident when going through a preempt/schedule cycle, meaning we don't lose any state. Cc: stable@vger.kernel.org Fixes: 8e01d9a396e6 ("KVM: arm64: vgic-v4: Move the GICv4 residency flow to be driven by vcpu_load/put") Reported-by: Xiang Chen Suggested-by: Zenghui Yu Tested-by: Xiang Chen Co-developed-by: Oliver Upton Signed-off-by: Marc Zyngier Acked-by: Zenghui Yu Link: https://lore.kernel.org/r/20230713070657.3873244-1-maz@kernel.org Signed-off-by: Oliver Upton --- arch/arm64/include/asm/kvm_host.h | 2 ++ arch/arm64/kvm/arm.c | 6 ++++-- arch/arm64/kvm/vgic/vgic-v3.c | 2 +- arch/arm64/kvm/vgic/vgic-v4.c | 7 +++++-- include/kvm/arm_vgic.h | 2 +- 5 files changed, 13 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 8b60967..d3dd05b 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -727,6 +727,8 @@ struct kvm_vcpu_arch { #define DBG_SS_ACTIVE_PENDING __vcpu_single_flag(sflags, BIT(5)) /* PMUSERENR for the guest EL0 is on physical CPU */ #define PMUSERENR_ON_CPU __vcpu_single_flag(sflags, BIT(6)) +/* WFI instruction trapped */ +#define IN_WFI __vcpu_single_flag(sflags, BIT(7)) /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */ diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index a402ea55..72dc53a7 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -718,13 +718,15 @@ void kvm_vcpu_wfi(struct kvm_vcpu *vcpu) */ preempt_disable(); kvm_vgic_vmcr_sync(vcpu); - vgic_v4_put(vcpu, true); + vcpu_set_flag(vcpu, IN_WFI); + vgic_v4_put(vcpu); preempt_enable(); kvm_vcpu_halt(vcpu); vcpu_clear_flag(vcpu, IN_WFIT); preempt_disable(); + vcpu_clear_flag(vcpu, IN_WFI); vgic_v4_load(vcpu); preempt_enable(); } @@ -792,7 +794,7 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu) if (kvm_check_request(KVM_REQ_RELOAD_GICv4, vcpu)) { /* The distributor enable bits were changed */ preempt_disable(); - vgic_v4_put(vcpu, false); + vgic_v4_put(vcpu); vgic_v4_load(vcpu); preempt_enable(); } diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c index c3b8e13..3dfc8b8 100644 --- a/arch/arm64/kvm/vgic/vgic-v3.c +++ b/arch/arm64/kvm/vgic/vgic-v3.c @@ -749,7 +749,7 @@ void vgic_v3_put(struct kvm_vcpu *vcpu) { struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3; - WARN_ON(vgic_v4_put(vcpu, false)); + WARN_ON(vgic_v4_put(vcpu)); vgic_v3_vmcr_sync(vcpu); diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c index c1c28fe..339a551 100644 --- a/arch/arm64/kvm/vgic/vgic-v4.c +++ b/arch/arm64/kvm/vgic/vgic-v4.c @@ -336,14 +336,14 @@ void vgic_v4_teardown(struct kvm *kvm) its_vm->vpes = NULL; } -int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db) +int vgic_v4_put(struct kvm_vcpu *vcpu) { struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe; if (!vgic_supports_direct_msis(vcpu->kvm) || !vpe->resident) return 0; - return its_make_vpe_non_resident(vpe, need_db); + return its_make_vpe_non_resident(vpe, !!vcpu_get_flag(vcpu, IN_WFI)); } int vgic_v4_load(struct kvm_vcpu *vcpu) @@ -354,6 +354,9 @@ int vgic_v4_load(struct kvm_vcpu *vcpu) if (!vgic_supports_direct_msis(vcpu->kvm) || vpe->resident) return 0; + if (vcpu_get_flag(vcpu, IN_WFI)) + return 0; + /* * Before making the VPE resident, make sure the redistributor * corresponding to our current CPU expects us here. See the diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h index 402b545..5b27f94 100644 --- a/include/kvm/arm_vgic.h +++ b/include/kvm/arm_vgic.h @@ -431,7 +431,7 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq, int vgic_v4_load(struct kvm_vcpu *vcpu); void vgic_v4_commit(struct kvm_vcpu *vcpu); -int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db); +int vgic_v4_put(struct kvm_vcpu *vcpu); /* CPU HP callbacks */ void kvm_vgic_cpu_up(void); -- 2.7.4