Currently, PSTATE.SS is set on every guest entry if single-step is enabled for the vCPU by userspace. However, it could cause extra single-step execution without returning to userspace, which shouldn't be performed, if the Software Step state at the last guest exit was Active-pending (i.e. the last exit was not triggered by Software Step exception, but by an asynchronous exception after the single-step execution is performed). Fix this by not setting PSTATE.SS on guest entry if the Software Step state at the last exit was Active-pending. Fixes: 337b99bf7edf ("KVM: arm64: guest debug, add support for single-step") Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx> --- arch/arm64/include/asm/kvm_host.h | 3 +++ arch/arm64/kvm/debug.c | 19 ++++++++++++++++++- arch/arm64/kvm/guest.c | 1 + arch/arm64/kvm/handle_exit.c | 2 ++ 4 files changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index e9c9388ccc02..4cf6eef02565 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -535,6 +535,9 @@ struct kvm_vcpu_arch { #define IN_WFIT __vcpu_single_flag(sflags, BIT(3)) /* vcpu system registers loaded on physical CPU */ #define SYSREGS_ON_CPU __vcpu_single_flag(sflags, BIT(4)) +/* Software step state is Active-pending */ +#define DBG_SS_ACTIVE_PENDING __vcpu_single_flag(sflags, BIT(5)) + /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */ #define vcpu_sve_pffr(vcpu) (kern_hyp_va((vcpu)->arch.sve_state) + \ diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c index 0b28d7db7c76..125cfb94b4ad 100644 --- a/arch/arm64/kvm/debug.c +++ b/arch/arm64/kvm/debug.c @@ -188,7 +188,16 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) * debugging the system. */ if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { - *vcpu_cpsr(vcpu) |= DBG_SPSR_SS; + /* + * If the software step state at the last guest exit + * was Active-pending, we don't set DBG_SPSR_SS so + * that the state is maintained (to not run another + * single-step until the pending Software Step + * exception is taken). + */ + if (!vcpu_get_flag(vcpu, DBG_SS_ACTIVE_PENDING)) + *vcpu_cpsr(vcpu) |= DBG_SPSR_SS; + mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); mdscr |= DBG_MDSCR_SS; vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); @@ -279,6 +288,14 @@ void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) &vcpu->arch.debug_ptr->dbg_wcr[0], &vcpu->arch.debug_ptr->dbg_wvr[0]); } + + if ((vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) && + !(*vcpu_cpsr(vcpu) & DBG_SPSR_SS)) + /* + * Mark the vcpu as ACTIVE_PENDING + * until Software Step exception is confirmed. + */ + vcpu_set_flag(vcpu, DBG_SS_ACTIVE_PENDING); } } diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index f802a3b3f8db..2ff13a3f8479 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -937,6 +937,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu, } else { /* If not enabled clear all flags */ vcpu->guest_debug = 0; + vcpu_clear_flag(vcpu, DBG_SS_ACTIVE_PENDING); } out: diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index bbe5b393d689..8e43b2668d67 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -154,6 +154,8 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu) if (ESR_ELx_EC(esr) == ESR_ELx_EC_WATCHPT_LOW) run->debug.arch.far = vcpu->arch.fault.far_el2; + else if (ESR_ELx_EC(esr) == ESR_ELx_EC_SOFTSTP_LOW) + vcpu_clear_flag(vcpu, DBG_SS_ACTIVE_PENDING); return 0; } -- 2.37.2.789.g6183377224-goog