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Subject[PATCH 5.4 108/110] KVM: arm64: Write arch.mdcr_el2 changes since last vcpu_load on VHE
From: Andrew Murray <>

commit 4942dc6638b07b5326b6d2faa142635c559e7cd5 upstream.

On VHE systems arch.mdcr_el2 is written to mdcr_el2 at vcpu_load time to
set options for self-hosted debug and the performance monitors

Unfortunately the value of arch.mdcr_el2 is not calculated until
kvm_arm_setup_debug() in the run loop after the vcpu has been loaded.
This means that the initial brief iterations of the run loop use a zero
value of mdcr_el2 - until the vcpu is preempted. This also results in a
delay between changes to vcpu->guest_debug taking effect.

Fix this by writing to mdcr_el2 in kvm_arm_setup_debug() on VHE systems
when a change to arch.mdcr_el2 has been detected.

Fixes: d5a21bcc2995 ("KVM: arm64: Move common VHE/non-VHE trap config in separate functions")
Cc: <> # 4.17.x-
Suggested-by: James Morse <>
Acked-by: Will Deacon <>
Reviewed-by: Marc Zyngier <>
Signed-off-by: Andrew Murray <>
Signed-off-by: Catalin Marinas <>
Signed-off-by: Greg Kroah-Hartman <>

arch/arm64/kvm/debug.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -101,7 +101,7 @@ void kvm_arm_reset_debug_ptr(struct kvm_
void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
- unsigned long mdscr;
+ unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;

trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);

@@ -197,6 +197,10 @@ void kvm_arm_setup_debug(struct kvm_vcpu
if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;

+ /* Write mdcr_el2 changes since vcpu_load on VHE systems */
+ if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
+ write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));

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