[PATCH v10 22/59] KVM: arm64: nv: Respect virtual CPTR_EL2.{TFP,FPEN} settings

[Marc Zyngier]

From: Jintack Lim <jintack.lim at linaro.org>

Forward traps due to FP/ASIMD register accesses to the virtual EL2
if virtual CPTR_EL2.TFP is set (with HCR_EL2.E2H == 0) or
CPTR_EL2.FPEN is configure to do so (with HCR_EL2.E2h == 1).

Signed-off-by: Jintack Lim <jintack.lim at linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall at arm.com>
[maz: account for HCR_EL2.E2H when testing for TFP/FPEN, with
 all the hard work actually being done by Chase Conklin]
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/kvm_emulate.h    | 25 +++++++++++++++++++++++++
 arch/arm64/kvm/handle_exit.c            | 16 ++++++++++++----
 arch/arm64/kvm/hyp/include/hyp/switch.h |  4 ++++
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 1ff0a224c32b..c64980d33c8b 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -11,6 +11,7 @@
 #ifndef __ARM64_KVM_EMULATE_H__
 #define __ARM64_KVM_EMULATE_H__
 
+#include <linux/bitfield.h>
 #include <linux/kvm_host.h>
 
 #include <asm/debug-monitors.h>
@@ -335,6 +336,30 @@ static inline bool vcpu_mode_priv(const struct kvm_vcpu *vcpu)
 	return mode != PSR_MODE_EL0t;
 }
 
+static inline bool guest_hyp_fpsimd_traps_enabled(const struct kvm_vcpu *vcpu)
+{
+	u64 val;
+
+	if (!vcpu_has_nv(vcpu))
+		return false;
+
+	val = vcpu_read_sys_reg(vcpu, CPTR_EL2);
+
+	if (!vcpu_el2_e2h_is_set(vcpu))
+		return (val & CPTR_EL2_TFP);
+
+	switch (FIELD_GET(CPACR_ELx_FPEN, val)) {
+	case 0b00:
+	case 0b10:
+		return true;
+	case 0b01:
+		return vcpu_el2_tge_is_set(vcpu) && !vcpu_is_el2(vcpu);
+	case 0b11:
+	default:		/* GCC is dumb */
+		return false;
+	}
+}
+
 static __always_inline u64 kvm_vcpu_get_esr(const struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.fault.esr_el2;
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 5811a791cf01..c4dc144726ee 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -87,11 +87,19 @@ static int handle_smc(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Guest access to FP/ASIMD registers are routed to this handler only
- * when the system doesn't support FP/ASIMD.
+ * This handles the cases where the system does not support FP/ASIMD or when
+ * we are running nested virtualization and the guest hypervisor is trapping
+ * FP/ASIMD accesses by its guest guest.
+ *
+ * All other handling of guest vs. host FP/ASIMD register state is handled in
+ * fixup_guest_exit().
  */
-static int handle_no_fpsimd(struct kvm_vcpu *vcpu)
+static int kvm_handle_fpasimd(struct kvm_vcpu *vcpu)
 {
+	if (guest_hyp_fpsimd_traps_enabled(vcpu))
+		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
+
+	/* This is the case when the system doesn't support FP/ASIMD. */
 	kvm_inject_undefined(vcpu);
 	return 1;
 }
@@ -253,7 +261,7 @@ static exit_handle_fn arm_exit_handlers[] = {
 	[ESR_ELx_EC_BREAKPT_LOW]= kvm_handle_guest_debug,
 	[ESR_ELx_EC_BKPT32]	= kvm_handle_guest_debug,
 	[ESR_ELx_EC_BRK64]	= kvm_handle_guest_debug,
-	[ESR_ELx_EC_FP_ASIMD]	= handle_no_fpsimd,
+	[ESR_ELx_EC_FP_ASIMD]	= kvm_handle_fpasimd,
 	[ESR_ELx_EC_PAC]	= kvm_handle_ptrauth,
 };
 
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index c6d62357e736..0a344184f26c 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -172,6 +172,10 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
 	if (!system_supports_fpsimd())
 		return false;
 
+	/* Forward traps to the guest hypervisor as required */
+	if (guest_hyp_fpsimd_traps_enabled(vcpu))
+		return false;
+
 	sve_guest = vcpu_has_sve(vcpu);
 	esr_ec = kvm_vcpu_trap_get_class(vcpu);
 
-- 
2.34.1