MIPS: KVM: Check MSA presence at uasm time

Check for presence of MSA at uasm assembly time rather than at runtime
in the generated KVM host entry code. This optimises the guest exit path
by eliminating the MSA code entirely if not present, and eliminating the
read of Config3.MSAP and conditional branch if MSA is present.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim KrÄmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/kvm/entry.c

@@ -55,7 +55,6 @@
 #define C0_CAUSE	13, 0
 #define C0_EPC		14, 0
 #define C0_EBASE	15, 1
-#define C0_CONFIG3	16, 3
 #define C0_CONFIG5	16, 5
 #define C0_DDATA_LO	28, 3
 #define C0_ERROREPC	30, 0
@@ -409,25 +408,21 @@ void *kvm_mips_build_exit(void *addr)
 		uasm_l_fpu_1(&l, p);
 	}
 
-#ifdef CONFIG_CPU_HAS_MSA
-	/*
-	 * If MSA is enabled, save MSACSR and clear it so that later
-	 * instructions don't trigger MSAFPE for pending exceptions.
-	 */
-	uasm_i_mfc0(&p, T0, C0_CONFIG3);
-	uasm_i_ext(&p, T0, T0, 28, 1); /* MIPS_CONF3_MSAP */
-	uasm_il_beqz(&p, &r, T0, label_msa_1);
-	 uasm_i_nop(&p);
-	uasm_i_mfc0(&p, T0, C0_CONFIG5);
-	uasm_i_ext(&p, T0, T0, 27, 1); /* MIPS_CONF5_MSAEN */
-	uasm_il_beqz(&p, &r, T0, label_msa_1);
-	 uasm_i_nop(&p);
-	uasm_i_cfcmsa(&p, T0, MSA_CSR);
-	uasm_i_sw(&p, T0, offsetof(struct kvm_vcpu_arch, fpu.msacsr),
-		  K1);
-	uasm_i_ctcmsa(&p, MSA_CSR, ZERO);
-	uasm_l_msa_1(&l, p);
-#endif
+	if (cpu_has_msa) {
+		/*
+		 * If MSA is enabled, save MSACSR and clear it so that later
+		 * instructions don't trigger MSAFPE for pending exceptions.
+		 */
+		uasm_i_mfc0(&p, T0, C0_CONFIG5);
+		uasm_i_ext(&p, T0, T0, 27, 1); /* MIPS_CONF5_MSAEN */
+		uasm_il_beqz(&p, &r, T0, label_msa_1);
+		 uasm_i_nop(&p);
+		uasm_i_cfcmsa(&p, T0, MSA_CSR);
+		uasm_i_sw(&p, T0, offsetof(struct kvm_vcpu_arch, fpu.msacsr),
+			  K1);
+		uasm_i_ctcmsa(&p, MSA_CSR, ZERO);
+		uasm_l_msa_1(&l, p);
+	}
 
 	/* Now that the new EBASE has been loaded, unset BEV and KSU_USER */
 	uasm_i_addiu(&p, AT, ZERO, ~(ST0_EXL | KSU_USER | ST0_IE));