x86/xen: properly retrieve NMI reason

Using the native code here can't work properly, as the hypervisor would
normally have cleared the two reason bits by the time Dom0 gets to see
the NMI (if passed to it at all). There's a shared info field for this,
and there's an existing hook to use - just fit the two together. This
is particularly relevant so that NMIs intended to be handled by APEI /
GHES actually make it to the respective handler.

Note that the hook can (and should) be used irrespective of whether
being in Dom0, as accessing port 0x61 in a DomU would be even worse,
while the shared info field would just hold zero all the time. Note
further that hardware NMI handling for PVH doesn't currently work
anyway due to missing code in the hypervisor (but it is expected to
work the native rather than the PV way).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index fac5e4f9607c..115016347806 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -40,6 +40,7 @@
 #include <xen/interface/physdev.h>
 #include <xen/interface/vcpu.h>
 #include <xen/interface/memory.h>
+#include <xen/interface/nmi.h>
 #include <xen/interface/xen-mca.h>
 #include <xen/features.h>
 #include <xen/page.h>
@@ -66,6 +67,7 @@
 #include <asm/reboot.h>
 #include <asm/stackprotector.h>
 #include <asm/hypervisor.h>
+#include <asm/mach_traps.h>
 #include <asm/mwait.h>
 #include <asm/pci_x86.h>
 #include <asm/pat.h>
@@ -1357,6 +1359,21 @@ static const struct machine_ops xen_machine_ops __initconst = {
         .emergency_restart = xen_emergency_restart,
 };
 
+static unsigned char xen_get_nmi_reason(void)
+{
+        unsigned char reason = 0;
+
+        /* Construct a value which looks like it came from port 0x61. */
+        if (test_bit(_XEN_NMIREASON_io_error,
+                     &HYPERVISOR_shared_info->arch.nmi_reason))
+                reason |= NMI_REASON_IOCHK;
+        if (test_bit(_XEN_NMIREASON_pci_serr,
+                     &HYPERVISOR_shared_info->arch.nmi_reason))
+                reason |= NMI_REASON_SERR;
+
+        return reason;
+}
+
 static void __init xen_boot_params_init_edd(void)
 {
 #if IS_ENABLED(CONFIG_EDD)
@@ -1541,9 +1558,12 @@ asmlinkage __visible void __init xen_start_kernel(void)
         pv_info = xen_info;
         pv_init_ops = xen_init_ops;
         pv_apic_ops = xen_apic_ops;
-        if (!xen_pvh_domain())
+        if (!xen_pvh_domain()) {
                 pv_cpu_ops = xen_cpu_ops;
 
+                x86_platform.get_nmi_reason = xen_get_nmi_reason;
+        }
+
         if (xen_feature(XENFEAT_auto_translated_physmap))
                 x86_init.resources.memory_setup = xen_auto_xlated_memory_setup;
         else