Allow swi_sched() to be called from NMI context.

For purposes of handling hardware error reported via NMIs I need a way to
escape NMI context, being too restrictive to do something significant.

To do it this change introduces new swi_sched() flag SWI_FROMNMI, making
it careful about used KPIs.  On platforms allowing IPI sending from NMI
context (x86 for now) it immediately wakes clk_intr_event via new IPI_SWI,
otherwise it works just like SWI_DELAY.  To handle the delayed SWIs this
patch calls clk_intr_event on every hardclock() tick.

MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.
Differential Revision:	https://reviews.freebsd.org/D25754

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/x86/xen/xen_apic.c b/sys/x86/xen/xen_apic.c
index 7d23f0a50417..78471eb1d997 100644
--- a/sys/x86/xen/xen_apic.c
+++ b/sys/x86/xen/xen_apic.c
@@ -76,6 +76,7 @@ static driver_filter_t xen_invlcache;
 static driver_filter_t xen_ipi_bitmap_handler;
 static driver_filter_t xen_cpustop_handler;
 static driver_filter_t xen_cpususpend_handler;
+static driver_filter_t xen_ipi_swi_handler;
 #endif
 
 /*---------------------------------- Macros ----------------------------------*/
@@ -103,6 +104,7 @@ static struct xen_ipi_handler xen_ipis[] =
 	[IPI_TO_IDX(IPI_BITMAP_VECTOR)] = { xen_ipi_bitmap_handler,	"b"   },
 	[IPI_TO_IDX(IPI_STOP)]		= { xen_cpustop_handler,	"st"  },
 	[IPI_TO_IDX(IPI_SUSPEND)]	= { xen_cpususpend_handler,	"sp"  },
+	[IPI_TO_IDX(IPI_SWI)]		= { xen_ipi_swi_handler,	"sw"  },
 };
 #endif
 
@@ -522,6 +524,15 @@ xen_cpususpend_handler(void *arg)
 	return (FILTER_HANDLED);
 }
 
+static int
+xen_ipi_swi_handler(void *arg)
+{
+	struct trapframe *frame = arg;
+
+	ipi_swi_handler(*frame);
+	return (FILTER_HANDLED);
+}
+
 /*----------------------------- XEN PV IPI setup -----------------------------*/
 /*
  * Those functions are provided outside of the Xen PV APIC implementation