linux-kernel - [PATCH 5.5 54/56] KVM: arm64: Write arch.mdcr_el2 changes since last vcpu

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Date:   Thu, 30 Jan 2020 19:39:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, James Morse <james.morse@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Andrew Murray <andrew.murray@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH 5.5 54/56] KVM: arm64: Write arch.mdcr_el2 changes since last vcpu_load on VHE

From: Andrew Murray <andrew.murray@....com>

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
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@...r.kernel.org> # 4.17.x-
Suggested-by: James Morse <james.morse@....com>
Acked-by: Will Deacon <will@...nel.org>
Reviewed-by: Marc Zyngier <maz@...nel.org>
Signed-off-by: Andrew Murray <andrew.murray@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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));
 }