LoongArch: KVM: Add LASX (256bit SIMD) support

This patch adds LASX (256bit SIMD) support for LoongArch KVM.

There will be LASX exception in KVM when guest use the LASX instructions.
KVM will enable LASX and restore the vector registers for guest and then
return to guest to continue running.
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/kvm_host.h

@@ -96,8 +96,9 @@ enum emulation_result {
 
 #define KVM_LARCH_FPU		(0x1 << 0)
 #define KVM_LARCH_LSX		(0x1 << 1)
-#define KVM_LARCH_SWCSR_LATEST	(0x1 << 2)
-#define KVM_LARCH_HWCSR_USABLE	(0x1 << 3)
+#define KVM_LARCH_LASX		(0x1 << 2)
+#define KVM_LARCH_SWCSR_LATEST	(0x1 << 3)
+#define KVM_LARCH_HWCSR_USABLE	(0x1 << 4)
 
 struct kvm_vcpu_arch {
 	/*
@@ -189,6 +190,11 @@ static inline bool kvm_guest_has_lsx(struct kvm_vcpu_arch *arch)
 	return arch->cpucfg[2] & CPUCFG2_LSX;
 }
 
+static inline bool kvm_guest_has_lasx(struct kvm_vcpu_arch *arch)
+{
+	return arch->cpucfg[2] & CPUCFG2_LASX;
+}
+
 /* Debug: dump vcpu state */
 int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu);
 

arch/loongarch/include/asm/kvm_vcpu.h

@@ -65,6 +65,16 @@ static inline void kvm_save_lsx(struct loongarch_fpu *fpu) { }
 static inline void kvm_restore_lsx(struct loongarch_fpu *fpu) { }
 #endif
 
+#ifdef CONFIG_CPU_HAS_LASX
+int kvm_own_lasx(struct kvm_vcpu *vcpu);
+void kvm_save_lasx(struct loongarch_fpu *fpu);
+void kvm_restore_lasx(struct loongarch_fpu *fpu);
+#else
+static inline int kvm_own_lasx(struct kvm_vcpu *vcpu) { }
+static inline void kvm_save_lasx(struct loongarch_fpu *fpu) { }
+static inline void kvm_restore_lasx(struct loongarch_fpu *fpu) { }
+#endif
+
 void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long hz);
 void kvm_reset_timer(struct kvm_vcpu *vcpu);
 void kvm_save_timer(struct kvm_vcpu *vcpu);

arch/loongarch/kernel/fpu.S

@@ -385,6 +385,7 @@ SYM_FUNC_START(_restore_lasx_upper)
 	lasx_restore_all_upper a0 t0 t1
 	jr	ra
 SYM_FUNC_END(_restore_lasx_upper)
+EXPORT_SYMBOL(_restore_lasx_upper)
 
 SYM_FUNC_START(_init_lasx_upper)
 	lasx_init_all_upper t1

arch/loongarch/kvm/exit.c

@@ -670,6 +670,21 @@ static int kvm_handle_lsx_disabled(struct kvm_vcpu *vcpu)
 	return RESUME_GUEST;
 }
 
+/*
+ * kvm_handle_lasx_disabled() - Guest used LASX while disabled in root.
+ * @vcpu:	Virtual CPU context.
+ *
+ * Handle when the guest attempts to use LASX when it is disabled in the root
+ * context.
+ */
+static int kvm_handle_lasx_disabled(struct kvm_vcpu *vcpu)
+{
+	if (kvm_own_lasx(vcpu))
+		kvm_queue_exception(vcpu, EXCCODE_INE, 0);
+
+	return RESUME_GUEST;
+}
+
 /*
  * LoongArch KVM callback handling for unimplemented guest exiting
  */
@@ -699,6 +714,7 @@ static exit_handle_fn kvm_fault_tables[EXCCODE_INT_START] = {
 	[EXCCODE_TLBM]			= kvm_handle_write_fault,
 	[EXCCODE_FPDIS]			= kvm_handle_fpu_disabled,
 	[EXCCODE_LSXDIS]		= kvm_handle_lsx_disabled,
+	[EXCCODE_LASXDIS]		= kvm_handle_lasx_disabled,
 	[EXCCODE_GSPR]			= kvm_handle_gspr,
 };
 

arch/loongarch/kvm/switch.S

@@ -261,6 +261,21 @@ SYM_FUNC_START(kvm_restore_lsx)
 SYM_FUNC_END(kvm_restore_lsx)
 #endif
 
+#ifdef CONFIG_CPU_HAS_LASX
+SYM_FUNC_START(kvm_save_lasx)
+	fpu_save_csr    a0 t1
+	fpu_save_cc     a0 t1 t2
+	lasx_save_data  a0 t1
+	jr              ra
+SYM_FUNC_END(kvm_save_lasx)
+
+SYM_FUNC_START(kvm_restore_lasx)
+	lasx_restore_data a0 t1
+	fpu_restore_cc    a0 t1 t2
+	fpu_restore_csr   a0 t1 t2
+	jr                ra
+SYM_FUNC_END(kvm_restore_lasx)
+#endif
 	.section ".rodata"
 SYM_DATA(kvm_exception_size, .quad kvm_exc_entry_end - kvm_exc_entry)
 SYM_DATA(kvm_enter_guest_size, .quad kvm_enter_guest_end - kvm_enter_guest)

arch/loongarch/kvm/trace.h

@@ -103,6 +103,7 @@ TRACE_EVENT(kvm_exit_gspr,
 
 #define KVM_TRACE_AUX_FPU		1
 #define KVM_TRACE_AUX_LSX		2
+#define KVM_TRACE_AUX_LASX		3
 
 #define kvm_trace_symbol_aux_op				\
 	{ KVM_TRACE_AUX_SAVE,		"save" },	\
@@ -113,7 +114,8 @@ TRACE_EVENT(kvm_exit_gspr,
 
 #define kvm_trace_symbol_aux_state			\
 	{ KVM_TRACE_AUX_FPU,     "FPU" },		\
-	{ KVM_TRACE_AUX_LSX,     "LSX" }
+	{ KVM_TRACE_AUX_LSX,     "LSX" },		\
+	{ KVM_TRACE_AUX_LASX,    "LASX" }
 
 TRACE_EVENT(kvm_aux,
 	    TP_PROTO(struct kvm_vcpu *vcpu, unsigned int op,

arch/loongarch/kvm/vcpu.c

@@ -317,6 +317,13 @@ static int _kvm_get_cpucfg(int id, u64 *v)
 		 */
 		if (cpu_has_lsx)
 			*v |= CPUCFG2_LSX;
+		/*
+		 * if LASX is supported by CPU, it is also supported by KVM,
+		 * as we implement it.
+		 */
+		if (cpu_has_lasx)
+			*v |= CPUCFG2_LASX;
+
 		break;
 	default:
 		ret = -EINVAL;
@@ -753,12 +760,54 @@ int kvm_own_lsx(struct kvm_vcpu *vcpu)
 }
 #endif
 
+#ifdef CONFIG_CPU_HAS_LASX
+/* Enable LASX and restore context */
+int kvm_own_lasx(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_guest_has_fpu(&vcpu->arch) || !kvm_guest_has_lsx(&vcpu->arch) || !kvm_guest_has_lasx(&vcpu->arch))
+		return -EINVAL;
+
+	preempt_disable();
+
+	set_csr_euen(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
+	switch (vcpu->arch.aux_inuse & (KVM_LARCH_FPU | KVM_LARCH_LSX)) {
+	case KVM_LARCH_LSX:
+	case KVM_LARCH_LSX | KVM_LARCH_FPU:
+		/* Guest LSX state already loaded, only restore upper LASX state */
+		_restore_lasx_upper(&vcpu->arch.fpu);
+		break;
+	case KVM_LARCH_FPU:
+		/* Guest FP state already loaded, only restore upper LSX & LASX state */
+		_restore_lsx_upper(&vcpu->arch.fpu);
+		_restore_lasx_upper(&vcpu->arch.fpu);
+		break;
+	default:
+		/* Neither FP or LSX already active, restore full LASX state */
+		kvm_restore_lasx(&vcpu->arch.fpu);
+		break;
+	}
+
+	trace_kvm_aux(vcpu, KVM_TRACE_AUX_RESTORE, KVM_TRACE_AUX_LASX);
+	vcpu->arch.aux_inuse |= KVM_LARCH_LASX | KVM_LARCH_LSX | KVM_LARCH_FPU;
+	preempt_enable();
+
+	return 0;
+}
+#endif
+
 /* Save context and disable FPU */
 void kvm_lose_fpu(struct kvm_vcpu *vcpu)
 {
 	preempt_disable();
 
-	if (vcpu->arch.aux_inuse & KVM_LARCH_LSX) {
+	if (vcpu->arch.aux_inuse & KVM_LARCH_LASX) {
+		kvm_save_lasx(&vcpu->arch.fpu);
+		vcpu->arch.aux_inuse &= ~(KVM_LARCH_LSX | KVM_LARCH_FPU | KVM_LARCH_LASX);
+		trace_kvm_aux(vcpu, KVM_TRACE_AUX_SAVE, KVM_TRACE_AUX_LASX);
+
+		/* Disable LASX & LSX & FPU */
+		clear_csr_euen(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
+	} else if (vcpu->arch.aux_inuse & KVM_LARCH_LSX) {
 		kvm_save_lsx(&vcpu->arch.fpu);
 		vcpu->arch.aux_inuse &= ~(KVM_LARCH_LSX | KVM_LARCH_FPU);
 		trace_kvm_aux(vcpu, KVM_TRACE_AUX_SAVE, KVM_TRACE_AUX_LSX);