When we are using the hardware registers for guest debug we need to deal
with the guests access to them. There is already a mechanism for dealing
with these accesses so we build on top of that.
- any access to mdscr_el1 is now stored in the mirror location
- access to DBG[WB][CV]R continues to go to guest's context
There is one register (MDCCINT_EL1) which guest debug doesn't care about
so this behaves as before.
Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
---
v3
- re-factor for better flow and fall through.
- much simpler with debug_ptr (use the guest area as before)
- tweak shadow fn to avoid multi-line if
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index a44fb32..7aa3b3a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -132,7 +132,13 @@ struct kvm_vcpu_arch {
* here.
*/
- /* Guest registers we preserve during guest debugging */
+ /*
+ * Guest registers we preserve during guest debugging.
+ *
+ * These shadow registers are updated by the kvm_handle_sys_reg
+ * trap handler if the guest accesses or updates them while we
+ * are using guest debug.
+ */
struct {
u32 pstate;
u32 mdscr_el1;
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 1ab63dd..dc8bca8 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -50,8 +50,7 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
{
*vcpu_cpsr(vcpu) |=
(vcpu->arch.guest_debug_state.pstate & SPSR_DEBUG_MASK);
- vcpu_sys_reg(vcpu, MDSCR_EL1) |=
- (vcpu->arch.guest_debug_state.mdscr_el1 & MDSCR_EL1_DEBUG_MASK);
+ vcpu_sys_reg(vcpu, MDSCR_EL1) = vcpu->arch.guest_debug_state.mdscr_el1;
}
/**
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c370b40..95f422f 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -196,11 +196,40 @@ static bool trap_dbgauthstatus_el1(struct kvm_vcpu *vcpu,
* - If the dirty bit is set, save guest registers, restore host
* registers and clear the dirty bit. This ensure that the host can
* now use the debug registers.
+ *
+ * We also use this mechanism to set-up the debug registers for guest
+ * debugging. If this is the case we want to ensure the guest sees
+ * the right versions of the registers - even if they are not going to
+ * be effective while guest debug is using HW debug.
+ *
*/
+
+static bool shadow_debug_reg(struct kvm_vcpu *vcpu,
+ const struct sys_reg_params *p,
+ const struct sys_reg_desc *r)
+{
+ /* MDSCR_EL1 */
+ if (r->reg == MDSCR_EL1) {
+ u32 *shadow_mdscr_el1 = &vcpu->arch.guest_debug_state.mdscr_el1;
+
+ if (p->is_write)
+ *shadow_mdscr_el1 = *vcpu_reg(vcpu, p->Rt);
+ else
+ *vcpu_reg(vcpu, p->Rt) = *shadow_mdscr_el1;
+
+ return true;
+ }
+
+ return false;
+}
+
static bool trap_debug_regs(struct kvm_vcpu *vcpu,
const struct sys_reg_params *p,
const struct sys_reg_desc *r)
{
+ if (vcpu->guest_debug && shadow_debug_reg(vcpu, p, r))
+ return true;
+
if (p->is_write) {
vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
--
2.3.5
--
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