[PATCH v4 07/18] KVM: arm64: Add {flush,sync}_hyp_timer_state() primitives

[Fuad Tabba <fuad.tabba@linux.dev>]

From: Marc Zyngier <maz@kernel.org>

A protected guest's virtual timer is programmed from EL2's own copy of
the state and read back there, so the host can't change the guest's
deadline. cntvoff_el2 is zeroed, so the guest's virtual time is the
physical time.

The flush also preserves the guest's CNTV and CNTP CVAL/CTL across the
host's full-context copy into the hyp vCPU, until the per-EC
marshalling patch removes that copy.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Co-developed-by: Fuad Tabba <fuad.tabba@linux.dev>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 41 ++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index b7b9f5afb673b..6f068d0f78d25 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -154,6 +154,35 @@ static void sync_hyp_vgic_state(struct pkvm_hyp_vcpu *hyp_vcpu)
 		host_cpu_if->vgic_lr[i] = hyp_cpu_if->vgic_lr[i];
 }
 
+static void flush_hyp_timer_state(struct pkvm_hyp_vcpu *hyp_vcpu)
+{
+	struct kvm_vcpu *vcpu = &hyp_vcpu->vcpu;
+
+	if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu))
+		return;
+
+	/* A hyp vcpu has no offset, and sees vtime == ptime. */
+	write_sysreg(0, cntvoff_el2);
+	write_sysreg_el0(__vcpu_sys_reg(vcpu, CNTV_CVAL_EL0), SYS_CNTV_CVAL);
+	isb();
+	write_sysreg_el0(__vcpu_sys_reg(vcpu, CNTV_CTL_EL0), SYS_CNTV_CTL);
+}
+
+static void sync_hyp_timer_state(struct pkvm_hyp_vcpu *hyp_vcpu)
+{
+	struct kvm_vcpu *vcpu = &hyp_vcpu->vcpu;
+
+	if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu))
+		return;
+
+	/*
+	 * Preserve the vtimer state so that it is always correct,
+	 * even if the host tries to make a mess.
+	 */
+	__vcpu_assign_sys_reg(vcpu, CNTV_CVAL_EL0, read_sysreg_el0(SYS_CNTV_CVAL));
+	__vcpu_assign_sys_reg(vcpu, CNTV_CTL_EL0, read_sysreg_el0(SYS_CNTV_CTL));
+}
+
 static void __copy_vcpu_state(const struct kvm_vcpu *from_vcpu,
 			      struct kvm_vcpu *to_vcpu)
 {
@@ -255,7 +284,17 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 		hyp_vcpu->vcpu.arch.mdcr_el2 = host_vcpu->arch.mdcr_el2;
 		hyp_vcpu->vcpu.arch.iflags = host_vcpu->arch.iflags;
 	} else {
+		u64 v_cval = hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTV_CVAL_EL0];
+		u64 v_ctl = hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTV_CTL_EL0];
+		u64 p_cval = hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTP_CVAL_EL0];
+		u64 p_ctl = hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTP_CTL_EL0];
+
 		hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt;
+
+		hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTV_CVAL_EL0] = v_cval;
+		hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTV_CTL_EL0] = v_ctl;
+		hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTP_CVAL_EL0] = p_cval;
+		hyp_vcpu->vcpu.arch.ctxt.sys_regs[CNTP_CTL_EL0] = p_ctl;
 	}
 
 	/* __hyp_running_vcpu must be NULL in a guest context. */
@@ -270,6 +309,7 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 	hyp_vcpu->vcpu.arch.vsesr_el2 = host_vcpu->arch.vsesr_el2;
 
 	flush_hyp_vgic_state(hyp_vcpu);
+	flush_hyp_timer_state(hyp_vcpu);
 
 	hyp_vcpu->vcpu.arch.pid = host_vcpu->arch.pid;
 
@@ -318,6 +358,7 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu, u32 exit_reason)
 	host_vcpu->arch.hcr_el2 |= hyp_vcpu->vcpu.arch.hcr_el2 & HCR_VSE;
 
 	sync_hyp_vgic_state(hyp_vcpu);
+	sync_hyp_timer_state(hyp_vcpu);
 
 	hyp_vcpu->exit_code = exit_reason;
 }
-- 
2.39.5