@@ -393,6 +393,7 @@ struct kvm_vcpu_arch {
*/
struct {
u32 mdscr_el1;
+ bool pstate_ss;
} guest_debug_preserved;
/* vcpu power state */
@@ -32,6 +32,10 @@ static DEFINE_PER_CPU(u64, mdcr_el2);
*
* Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
* after we have restored the preserved value to the main context.
+ *
+ * When single-step is enabled by userspace, we tweak PSTATE.SS on every
+ * guest entry. Preserve PSTATE.SS so we can restore the original value
+ * for the vcpu after the single-step is disabled.
*/
static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
{
@@ -41,6 +45,9 @@ static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
vcpu->arch.guest_debug_preserved.mdscr_el1);
+
+ vcpu->arch.guest_debug_preserved.pstate_ss =
+ (*vcpu_cpsr(vcpu) & DBG_SPSR_SS);
}
static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
@@ -51,6 +58,11 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
vcpu_read_sys_reg(vcpu, MDSCR_EL1));
+
+ if (vcpu->arch.guest_debug_preserved.pstate_ss)
+ *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
+ else
+ *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
}
/**
Preserve the PSTATE.SS value for the guest while userspace enables single-step (i.e. while KVM manipulates the PSTATE.SS) for the vCPU. Currently, while userspace enables single-step for the vCPU (with KVM_GUESTDBG_SINGLESTEP), KVM sets PSTATE.SS to 1 on every guest entry, not saving its original value. When userspace disables single-step, KVM doesn't restore the original value for the subsequent guest entry (use the current value instead). Exception return instructions copy PSTATE.SS from SPSR_ELx.SS only in certain cases when single-step is enabled (and set it to 0 in other cases). So, the value matters only when the guest enables single-step (and when the guest's Software step state isn't affected by single-step enabled by userspace, practically), though. Fix this by preserving the original PSTATE.SS value while userspace enables single-step, and restoring the value once it is disabled. This fix modifies the behavior of GET_ONE_REG/SET_ONE_REG for the PSTATE.SS while single-step is enabled by userspace. Presently, GET_ONE_REG/SET_ONE_REG gets/sets the current PSTATE.SS value, which KVM will override on the next guest entry (i.e. the value userspace gets/sets is not used for the next guest entry). With this patch, GET_ONE_REG/SET_ONE_REG will get/set the guest's preserved value, which KVM will preserve and try to restore after single-step is disabled. Fixes: 337b99bf7edf ("KVM: arm64: guest debug, add support for single-step") Signed-off-by: Reiji Watanabe <reijiw@google.com> --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/debug.c | 12 ++++++++++++ 2 files changed, 13 insertions(+)