KVM: arm64: Use the xarray as the primary sysreg/sysinsn walker

Since we always start sysreg/sysinsn handling by searching the
xarray, use it as the source of the index in the correct sys_reg_desc
array.

This allows some cleanup, such as moving the handling of unknown
sysregs in a single location.
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240214131827.2856277-16-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_nested.h

@@ -60,7 +60,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
 	return ttbr0 & ~GENMASK_ULL(63, 48);
 }
 
-extern bool __check_nv_sr_forward(struct kvm_vcpu *vcpu);
+extern bool __check_nv_sr_forward(struct kvm_vcpu *vcpu, int *sr_idx);
 
 int kvm_init_nv_sysregs(struct kvm *kvm);
 

arch/arm64/kvm/emulate-nested.c

@@ -2007,7 +2007,7 @@ static bool check_fgt_bit(struct kvm *kvm, bool is_read,
 	return !(kvm_get_sysreg_res0(kvm, sr) & BIT(tc.bit));
 }
 
-bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
+bool __check_nv_sr_forward(struct kvm_vcpu *vcpu, int *sr_index)
 {
 	union trap_config tc;
 	enum trap_behaviour b;
@@ -2015,9 +2015,6 @@ bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
 	u32 sysreg;
 	u64 esr, val;
 
-	if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
-		return false;
-
 	esr = kvm_vcpu_get_esr(vcpu);
 	sysreg = esr_sys64_to_sysreg(esr);
 	is_read = (esr & ESR_ELx_SYS64_ISS_DIR_MASK) == ESR_ELx_SYS64_ISS_DIR_READ;
@@ -2028,13 +2025,16 @@ bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
 	 * A value of 0 for the whole entry means that we know nothing
 	 * for this sysreg, and that it cannot be re-injected into the
 	 * nested hypervisor. In this situation, let's cut it short.
-	 *
-	 * Note that ultimately, we could also make use of the xarray
-	 * to store the index of the sysreg in the local descriptor
-	 * array, avoiding another search... Hint, hint...
 	 */
 	if (!tc.val)
-		return false;
+		goto local;
+
+	/*
+	 * If we're not nesting, immediately return to the caller, with the
+	 * sysreg index, should we have it.
+	 */
+	if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
+		goto local;
 
 	switch ((enum fgt_group_id)tc.fgt) {
 	case __NO_FGT_GROUP__:
@@ -2076,7 +2076,7 @@ bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
 	case __NR_FGT_GROUP_IDS__:
 		/* Something is really wrong, bail out */
 		WARN_ONCE(1, "__NR_FGT_GROUP_IDS__");
-		return false;
+		goto local;
 	}
 
 	if (tc.fgt != __NO_FGT_GROUP__ && check_fgt_bit(vcpu->kvm, is_read,
@@ -2089,6 +2089,26 @@ bool __check_nv_sr_forward(struct kvm_vcpu *vcpu)
 	    ((b & BEHAVE_FORWARD_WRITE) && !is_read))
 		goto inject;
 
+local:
+	if (!tc.sri) {
+		struct sys_reg_params params;
+
+		params = esr_sys64_to_params(esr);
+
+		/*
+		 * Check for the IMPDEF range, as per DDI0487 J.a,
+		 * D18.3.2 Reserved encodings for IMPLEMENTATION
+		 * DEFINED registers.
+		 */
+		if (!(params.Op0 == 3 && (params.CRn & 0b1011) == 0b1011))
+			print_sys_reg_msg(&params,
+					  "Unsupported guest access at: %lx\n",
+					  *vcpu_pc(vcpu));
+		kvm_inject_undefined(vcpu);
+		return true;
+	}
+
+	*sr_index = tc.sri - 1;
 	return false;
 
 inject:

arch/arm64/kvm/sys_regs.c

@@ -3395,12 +3395,6 @@ int kvm_handle_cp14_32(struct kvm_vcpu *vcpu)
 	return kvm_handle_cp_32(vcpu, &params, cp14_regs, ARRAY_SIZE(cp14_regs));
 }
 
-static bool is_imp_def_sys_reg(struct sys_reg_params *params)
-{
-	// See ARM DDI 0487E.a, section D12.3.2
-	return params->Op0 == 3 && (params->CRn & 0b1011) == 0b1011;
-}
-
 /**
  * emulate_sys_reg - Emulate a guest access to an AArch64 system register
  * @vcpu: The VCPU pointer
@@ -3414,39 +3408,17 @@ static bool emulate_sys_reg(struct kvm_vcpu *vcpu,
 	const struct sys_reg_desc *r;
 
 	r = find_reg(params, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
-
 	if (likely(r)) {
 		perform_access(vcpu, params, r);
 		return true;
 	}
 
-	if (is_imp_def_sys_reg(params)) {
-		kvm_inject_undefined(vcpu);
-	} else {
 	print_sys_reg_msg(params,
 			  "Unsupported guest sys_reg access at: %lx [%08lx]\n",
 			  *vcpu_pc(vcpu), *vcpu_cpsr(vcpu));
 	kvm_inject_undefined(vcpu);
-	}
-	return false;
-}
-
-static int emulate_sys_instr(struct kvm_vcpu *vcpu, struct sys_reg_params *p)
-{
-	const struct sys_reg_desc *r;
 
-	/* Search from the system instruction table. */
-	r = find_reg(p, sys_insn_descs, ARRAY_SIZE(sys_insn_descs));
-
-	if (likely(r)) {
-		perform_access(vcpu, p, r);
-	} else {
-		kvm_err("Unsupported guest sys instruction at: %lx\n",
-			*vcpu_pc(vcpu));
-		print_sys_reg_instr(p);
-		kvm_inject_undefined(vcpu);
-	}
-	return 1;
+	return false;
 }
 
 static void kvm_reset_id_regs(struct kvm_vcpu *vcpu)
@@ -3502,31 +3474,34 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
  */
 int kvm_handle_sys_reg(struct kvm_vcpu *vcpu)
 {
+	const struct sys_reg_desc *desc = NULL;
 	struct sys_reg_params params;
 	unsigned long esr = kvm_vcpu_get_esr(vcpu);
 	int Rt = kvm_vcpu_sys_get_rt(vcpu);
+	int sr_idx;
 
 	trace_kvm_handle_sys_reg(esr);
 
-	if (__check_nv_sr_forward(vcpu))
+	if (__check_nv_sr_forward(vcpu, &sr_idx))
 		return 1;
 
 	params = esr_sys64_to_params(esr);
 	params.regval = vcpu_get_reg(vcpu, Rt);
 
 	/* System registers have Op0=={2,3}, as per DDI487 J.a C5.1.2 */
-	if (params.Op0 == 2 || params.Op0 == 3) {
-		if (!emulate_sys_reg(vcpu, &params))
-			return 1;
+	if (params.Op0 == 2 || params.Op0 == 3)
+		desc = &sys_reg_descs[sr_idx];
+	else
+		desc = &sys_insn_descs[sr_idx];
 
-		if (!params.is_write)
+	perform_access(vcpu, &params, desc);
+
+	/* Read from system register? */
+	if (!params.is_write &&
+	    (params.Op0 == 2 || params.Op0 == 3))
 		vcpu_set_reg(vcpu, Rt, params.regval);
 
 	return 1;
-	}
-
-	/* Hints, PSTATE (Op0 == 0) and System instructions (Op0 == 1) */
-	return emulate_sys_instr(vcpu, &params);
 }
 
 /******************************************************************************