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

Alex Bennée
2015-03-31T15:01:26Z

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@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

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