[PATCH v2 09/10] KVM: arm64: trap nested debug register access

[Alex Bennée]

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.

  - mdscr_el1_bits is renamed as we save the whole register
  - any access to mdscr_el1 is now stored in the mirror location
  - if we are using HW assisted debug we do the same with DBG[WB][CV]R

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 at linaro.org>

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2c359c9..3d32d45 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -122,10 +122,13 @@ struct kvm_vcpu_arch {
 	 * here.
 	 */
 
-	/* Registers pre any guest debug manipulations */
+	/* Registers before any guest debug manipulations. These
+	 * shadow registers are updated by the kvm_handle_sys_reg
+	 * trap handler if the guest accesses or updates them
+	 */
 	struct {
 		u32	pstate_ss_bit;
-		u32	mdscr_el1_bits;
+		u32	mdscr_el1;
 
 		struct kvm_guest_debug_arch debug_regs;
 	} debug_saved_regs;
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 3b368f3..638c111 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -55,8 +55,6 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
 	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | MDCR_EL2_TPMCR);
 	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TDRA | MDCR_EL2_TDOSA);
 
-	trace_kvm_arch_setup_debug_reg32("MDCR_EL2", vcpu->arch.mdcr_el2);
-
 	/*
 	 * If we are not treating debug registers are dirty we need
 	 * to trap if the guest starts accessing them.
@@ -71,8 +69,10 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
 		/* Save pstate/mdscr */
 		vcpu_debug_saved_reg(vcpu, pstate_ss_bit) =
 			*vcpu_cpsr(vcpu) & DBG_SPSR_SS;
-		vcpu_debug_saved_reg(vcpu, mdscr_el1_bits) =
-			vcpu_sys_reg(vcpu, MDSCR_EL1) & MDSCR_EL1_DEBUG_BITS;
+
+		vcpu_debug_saved_reg(vcpu, mdscr_el1) =
+			vcpu_sys_reg(vcpu, MDSCR_EL1);
+
 		/*
 		 * Single Step (ARM ARM D2.12.3 The software step state
 		 * machine)
@@ -161,9 +161,8 @@ void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
 		*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
 		*vcpu_cpsr(vcpu) |= vcpu_debug_saved_reg(vcpu, pstate_ss_bit);
 
-		vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~MDSCR_EL1_DEBUG_BITS;
-		vcpu_sys_reg(vcpu, MDSCR_EL1) |=
-			vcpu_debug_saved_reg(vcpu, mdscr_el1_bits);
+		vcpu_sys_reg(vcpu, MDSCR_EL1) =
+			vcpu_debug_saved_reg(vcpu, mdscr_el1);
 
 		/*
 		 * If we were using HW debug we need to restore the
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index be9b188..d43d7d1 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -208,39 +208,61 @@ 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 & KVM_GUESTDBG_USE_HW_BP) {
-		struct kvm_guest_debug_arch *saved;
-		__u64 *val;
-
-		saved = &vcpu_debug_saved_reg(vcpu, debug_regs);
-
-		if (r->reg >= DBGBCR0_EL1 && r->reg <= DBGBCR15_EL1)
-			val = &saved->dbg_bcr[r->reg - DBGBCR0_EL1];
-		else if (r->reg >= DBGBVR0_EL1 && r->reg <= DBGBVR15_EL1)
-			val = &saved->dbg_bvr[r->reg - DBGBVR0_EL1];
-		else if (r->reg >= DBGWCR0_EL1 && r->reg <= DBGWCR15_EL1)
-			val = &saved->dbg_wcr[r->reg - DBGWCR0_EL1];
-		else if (r->reg >= DBGWVR0_EL1 && r->reg <= DBGWVR15_EL1)
-			val = &saved->dbg_wvr[r->reg - DBGWVR0_EL1];
-		else {
-			kvm_err("Bad register index %d\n", r->reg);
-			return false;
+	if (vcpu->guest_debug) {
+
+		/* MDSCR_EL1 */
+		if (r->reg == MDSCR_EL1) {
+			if (p->is_write)
+				vcpu_debug_saved_reg(vcpu, mdscr_el1) =
+					*vcpu_reg(vcpu, p->Rt);
+			else
+				*vcpu_reg(vcpu, p->Rt) =
+					vcpu_debug_saved_reg(vcpu, mdscr_el1);
+
+			return true;
 		}
 
-		if (p->is_write)
-			*val = *vcpu_reg(vcpu, p->Rt);
-		else
-			*vcpu_reg(vcpu, p->Rt) = *val;
+		/* MDCCINT_EL1 */
+		if (r->reg == MDCCINT_EL1)
+			goto old;
+
+		/* We only shadow DBG* if guest being debugged */
+		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+			struct kvm_guest_debug_arch *saved;
+			__u64 *val;
+
+			saved = &vcpu_debug_saved_reg(vcpu, debug_regs);
+
+			if (r->reg >= DBGBCR0_EL1 && r->reg <= DBGBCR15_EL1)
+				val = &saved->dbg_bcr[r->reg - DBGBCR0_EL1];
+			else if (r->reg >= DBGBVR0_EL1 && r->reg <= DBGBVR15_EL1)
+				val = &saved->dbg_bvr[r->reg - DBGBVR0_EL1];
+			else if (r->reg >= DBGWCR0_EL1 && r->reg <= DBGWCR15_EL1)
+				val = &saved->dbg_wcr[r->reg - DBGWCR0_EL1];
+			else if (r->reg >= DBGWVR0_EL1 && r->reg <= DBGWVR15_EL1)
+				val = &saved->dbg_wvr[r->reg - DBGWVR0_EL1];
+			else {
+				kvm_err("Bad register index %d\n", r->reg);
+				return false;
+			}
 
-	} else {
-		if (p->is_write) {
-			vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
-			vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
-		} else {
-			*vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, r->reg);
+			if (p->is_write)
+				*val = *vcpu_reg(vcpu, p->Rt);
+			else
+				*vcpu_reg(vcpu, p->Rt) = *val;
+
+			return true;
 		}
 	}
 
+old:
+	if (p->is_write) {
+		vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
+		vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
+	} else {
+		*vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, r->reg);
+	}
+
 	return true;
 }
 
-- 
2.3.4