[PATCH 3/4] KVM: arm64: nv: Add additional trap setup for CPTR_EL2

[Marc Zyngier <maz@kernel.org>]

We need to teach KVM a couple of new tricks. CPTR_EL2 and its
VHE accessor CPACR_EL1 need to be handled specially:

- CPACR_EL1 is trapped on VHE so that we can track the TCPAC
  and TTA bits

- CPTR_EL2.{TCPAC,E0POE} are propagated from L1 to L2

As a consequence of CPTR_EL2 being always trapped, we update
vcpu_sanitised_cptr_el2() so that it doesn't try to read from
the CPU registers, but from the shadow copy (ensuring that we
always have up-to-date TCPAC and TTA bits).

This helper will also be used when handling the CPTR_EL1 trap.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_emulate.h |  2 +-
 arch/arm64/kvm/hyp/vhe/switch.c      | 23 ++++++++++++++++++++++-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index e86de04ba1c4..cc5c93b46e6f 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -607,7 +607,7 @@ static __always_inline void kvm_reset_cptr_el2(struct kvm_vcpu *vcpu)
  */
 static inline u64 vcpu_sanitised_cptr_el2(const struct kvm_vcpu *vcpu)
 {
-	u64 cptr = vcpu_read_sys_reg(vcpu, CPTR_EL2);
+	u64 cptr = __vcpu_sys_reg(vcpu, CPTR_EL2);
 
 	if (!vcpu_el2_e2h_is_set(vcpu))
 		cptr = translate_cptr_el2_to_cpacr_el1(cptr);
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index d07b4f4be5e5..b4ba236526d6 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -67,6 +67,8 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu)
 
 static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
 {
+	u64 cptr;
+
 	/*
 	 * With VHE (HCR.E2H == 1), accesses to CPACR_EL1 are routed to
 	 * CPTR_EL2. In general, CPACR_EL1 has the same layout as CPTR_EL2,
@@ -85,11 +87,23 @@ static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
 		__activate_traps_fpsimd32(vcpu);
 	}
 
+	if (!vcpu_has_nv(vcpu))
+		goto write;
+
+	/*
+	 * The architecture is a bit crap (what a surprise): an EL2 guest
+	 * writing to CPTR_EL2 via CPACR_EL1 can't set any of TCPAC or TTA,
+	 * as they are RES0 in the guest's view. To work around it, trap the
+	 * sucker using the very same bit it can't set...
+	 */
+	if (vcpu_el2_e2h_is_set(vcpu) && is_hyp_ctxt(vcpu))
+		val |= CPTR_EL2_TCPAC;
+
 	/*
 	 * Layer the guest hypervisor's trap configuration on top of our own if
 	 * we're in a nested context.
 	 */
-	if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
+	if (is_hyp_ctxt(vcpu))
 		goto write;
 
 	if (guest_hyp_fpsimd_traps_enabled(vcpu))
@@ -97,6 +111,13 @@ static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
 	if (guest_hyp_sve_traps_enabled(vcpu))
 		val &= ~CPACR_ELx_ZEN;
 
+	cptr = vcpu_sanitised_cptr_el2(vcpu);
+
+	if (kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, S2POE, IMP))
+		val |= cptr & CPACR_ELx_E0POE;
+
+	val |= cptr & CPTR_EL2_TCPAC;
+
 write:
 	write_sysreg(val, cpacr_el1);
 }
-- 
2.39.2


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