[PATCH 2/2] xen/x86: introduce AMD_MCE_NONFATAL

[Stefano Stabellini <stefano.stabellini@xxxxxxx>]

Today, checking for non-fatal MCE errors on ARM is very invasive: it
involves a periodic timer interrupting the physical CPU execution at
regular intervals. Moreover, when the timer fires, the handler sends an
IPI to all physical CPUs.

Both these actions are disruptive in terms of latency and deterministic
execution times for real-time workloads. They might miss a deadline due
to one of these IPIs. Make it possible to disable non-fatal MCE errors
checking with a new Kconfig option (AMD_MCE_NONFATAL).

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
---
RFC. I couldn't find a better way to do this.
---
 xen/arch/x86/Kconfig.cpu               | 15 +++++++++++++++
 xen/arch/x86/cpu/mcheck/amd_nonfatal.c |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/Kconfig.cpu b/xen/arch/x86/Kconfig.cpu
index 5fb18db1aa..14e20ad19d 100644
--- a/xen/arch/x86/Kconfig.cpu
+++ b/xen/arch/x86/Kconfig.cpu
@@ -10,6 +10,21 @@ config AMD
          May be turned off in builds targetting other vendors.  Otherwise,
          must be enabled for Xen to work suitably on AMD platforms.
 
+config AMD_MCE_NONFATAL
+       bool "Check for non-fatal MCEs on AMD CPUs"
+       default y
+       depends on AMD
+       help
+         Check for non-fatal MCE errors.
+
+         When this option is on (default), Xen regularly checks for
+         non-fatal MCEs potentially occurring on all physical CPUs. The
+         checking is done via timers and IPI interrupts, which is
+         acceptable in most configurations, but not for real-time.
+
+         Turn this option off if you plan on deploying real-time workloads
+         on Xen.
+
 config INTEL
        bool "Support Intel CPUs"
        default y
diff --git a/xen/arch/x86/cpu/mcheck/amd_nonfatal.c 
b/xen/arch/x86/cpu/mcheck/amd_nonfatal.c
index 7d48c9ab5f..812e18f612 100644
--- a/xen/arch/x86/cpu/mcheck/amd_nonfatal.c
+++ b/xen/arch/x86/cpu/mcheck/amd_nonfatal.c
@@ -191,7 +191,8 @@ static void cf_check mce_amd_work_fn(void *data)
 
 void __init amd_nonfatal_mcheck_init(struct cpuinfo_x86 *c)
 {
-       if (!(c->x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON)))
+       if ( !IS_ENABLED(CONFIG_AMD_MCE_NONFATAL) ||
+            (!(c->x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON))) )
                return;
 
        /* Assume we are on K8 or newer AMD or Hygon CPU here */
-- 
2.25.1