[Bionic] KVM: arm64: Write arch.mdcr_el2 changes since last vcpu_load on VHE

[Thadeu Lima de Souza Cascardo]

From: Andrew Murray <andrew.murray at arm.com>

BugLink: https://bugs.launchpad.net/bugs/1860657

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
extension.

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: <stable at vger.kernel.org> # 4.17.x-
Suggested-by: James Morse <james.morse at arm.com>
Acked-by: Will Deacon <will at kernel.org>
Reviewed-by: Marc Zyngier <maz at kernel.org>
Signed-off-by: Andrew Murray <andrew.murray at arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
(backported from commit 4942dc6638b07b5326b6d2faa142635c559e7cd5)
[cascardo: backport considering context and changes up to 5.0]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 arch/arm64/kvm/debug.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index fa63b28c65e0..87ed43c941de 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -108,6 +108,7 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 {
 	bool trap_debug = !(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY);
+	unsigned long orig_mdcr_el2 = vcpu->arch.mdcr_el2;
 
 	trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
 
@@ -193,6 +194,10 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 	if (trap_debug)
 		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
 
+	/* 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_sys_reg(vcpu, MDSCR_EL1));
 }
-- 
2.24.0