xen/arm: Warn user on cpu errata 832075

When a Cortex A57 processor is affected by CPU errata 832075, a guest
not implementing the workaround for it could deadlock the system.
Add a warning during boot informing the user that only trusted guests
should be executed on the system.
An equivalent warning is already given to the user by KVM on cores
affected by this errata.

Also taint the hypervisor as unsecure when this errata applies and
mention Cortex A57 r0p0 - r1p2 as not security supported in SUPPORT.md

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
[fix SUPPORT.md style, 3 printk lines instead of 4]
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>

SUPPORT.md

@@ -38,6 +38,9 @@ supported in this document.
 ### ARM v8
 
     Status: Supported
+    Status, Cortex A57 r0p0-r1p1: Supported, not security supported
+
+For the Cortex A57 r0p0 - r1p1, see Errata 832075.
 
 ## Host hardware support
 

xen/arch/arm/cpuerrata.c

@@ -503,6 +503,18 @@ void check_local_cpu_errata(void)
 void __init enable_errata_workarounds(void)
 {
     enable_cpu_capabilities(arm_errata);
+
+#ifdef CONFIG_ARM64_ERRATUM_832075
+    if ( cpus_have_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) )
+    {
+        printk_once("**** This CPU is affected by the errata 832075.                      ****\n"
+                    "**** Guests without CPU erratum workarounds can deadlock the system! ****\n"
+                    "**** Only trusted guests should be used.                             ****\n");
+
+        /* Taint the machine has being insecure */
+        add_taint(TAINT_MACHINE_UNSECURE);
+    }
+#endif
 }
 
 static int cpu_errata_callback(struct notifier_block *nfb,