Use PFR0 to identify need for mitigation of CVE-2017-5715

If the CSV2 field reads as 1 then branch targets trained in one
context cannot affect speculative execution in a different context.
In that case skip the workaround on Cortex A72 and A73.

Change-Id: Ide24fb6efc77c548e4296295adc38dca87d042ee
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

include/lib/cpus/aarch64/cpu_macros.S

@@ -229,3 +229,18 @@ CPU_OPS_SIZE = .
 #endif
 
 #endif /* __CPU_MACROS_S__ */
+
+	/*
+	 * This macro is used on some CPUs to detect if they are vulnerable
+	 * to CVE-2017-5715.
+	 */
+	.macro	cpu_check_csv2 _reg _label
+	mrs	\_reg, id_aa64pfr0_el1
+	ubfx	\_reg, \_reg, #ID_AA64PFR0_CSV2_SHIFT, #ID_AA64PFR0_CSV2_LENGTH
+	/*
+	 * If the field equals to 1 then branch targets trained in one
+	 * context cannot affect speculative execution in a different context.
+	 */
+	cmp	\_reg, #1
+	beq	\_label
+	.endm

lib/cpus/aarch64/cortex_a72.S

@@ -98,12 +98,16 @@ func check_errata_859971
 endfunc check_errata_859971
 
 func check_errata_cve_2017_5715
+	cpu_check_csv2	x0, 1f
 #if WORKAROUND_CVE_2017_5715
 	mov	x0, #ERRATA_APPLIES
 #else
 	mov	x0, #ERRATA_MISSING
 #endif
 	ret
+1:
+	mov	x0, #ERRATA_NOT_APPLIES
+	ret
 endfunc check_errata_cve_2017_5715
 
 	/* -------------------------------------------------
@@ -121,8 +125,10 @@ func cortex_a72_reset_func
 #endif
 
 #if IMAGE_BL31 && WORKAROUND_CVE_2017_5715
+	cpu_check_csv2	x0, 1f
 	adr	x0, workaround_mmu_runtime_exceptions
 	msr	vbar_el3, x0
+1:
 #endif
 
 	/* ---------------------------------------------

lib/cpus/aarch64/cortex_a73.S

@@ -37,8 +37,10 @@ endfunc cortex_a73_disable_smp
 
 func cortex_a73_reset_func
 #if IMAGE_BL31 && WORKAROUND_CVE_2017_5715
+	cpu_check_csv2	x0, 1f
 	adr	x0, workaround_bpiall_vbar0_runtime_exceptions
 	msr	vbar_el3, x0
+1:
 #endif
 
 	/* ---------------------------------------------
@@ -115,12 +117,16 @@ func cortex_a73_cluster_pwr_dwn
 endfunc cortex_a73_cluster_pwr_dwn
 
 func check_errata_cve_2017_5715
+	cpu_check_csv2	x0, 1f
 #if WORKAROUND_CVE_2017_5715
 	mov	x0, #ERRATA_APPLIES
 #else
 	mov	x0, #ERRATA_MISSING
 #endif
 	ret
+1:
+	mov	x0, #ERRATA_NOT_APPLIES
+	ret
 endfunc check_errata_cve_2017_5715
 
 #if REPORT_ERRATA

lib/cpus/aarch64/cortex_a75.S

@@ -12,15 +12,7 @@
 
 func cortex_a75_reset_func
 #if IMAGE_BL31 && WORKAROUND_CVE_2017_5715
-	mrs	x0, id_aa64pfr0_el1
-	ubfx	x0, x0, #ID_AA64PFR0_CSV2_SHIFT, #ID_AA64PFR0_CSV2_LENGTH
-	/*
-	 * If the field equals to 1 then branch targets trained in one
-	 * context cannot affect speculative execution in a different context.
-	 */
-	cmp	x0, #1
-	beq	1f
-
+	cpu_check_csv2	x0, 1f
 	adr	x0, workaround_bpiall_vbar0_runtime_exceptions
 	msr	vbar_el3, x0
 1:
@@ -53,15 +45,7 @@ func cortex_a75_reset_func
 endfunc cortex_a75_reset_func
 
 func check_errata_cve_2017_5715
-	mrs	x0, id_aa64pfr0_el1
-	ubfx	x0, x0, #ID_AA64PFR0_CSV2_SHIFT, #ID_AA64PFR0_CSV2_LENGTH
-	/*
-	 * If the field equals to 1 then branch targets trained in one
-	 * context cannot affect speculative execution in a different context.
-	 */
-	cmp	x0, #1
-	beq	1f
-
+	cpu_check_csv2	x0, 1f
 #if WORKAROUND_CVE_2017_5715
 	mov	x0, #ERRATA_APPLIES
 #else