irqchip/gic-v3-its: Use pre-programmed redistributor tables with kdump kernels

commit c6e2ccb66d0c3b4fffc59932585e9f709ad59003 upstream

If using a kdump kernel, and that we cannot disable LPIs to install
our own tables, let's switch to using the already allocated tables.

This means that we'll change some of the initial kernel's memory,
but at least we'll be able to have LPIs in this secondary kernel.
Tested-by: NJeremy Linton <jeremy.linton@arm.com>
Tested-by: NBhupesh Sharma <bhsharma@redhat.com>
Tested-by: NLei Zhang <zhang.lei@jp.fujitsu.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NZou Cao <zoucao@linux.alibaba.com>
Reviewed-by: NBaoyou Xie <xie.baoyou@linux.alibaba.com>

drivers/irqchip/irq-gic-v3-its.c

@@ -19,6 +19,7 @@
 #include <linux/acpi_iort.h>
 #include <linux/bitmap.h>
 #include <linux/cpu.h>
+#include <linux/crash_dump.h>
 #include <linux/delay.h>
 #include <linux/dma-iommu.h>
 #include <linux/interrupt.h>
@@ -2006,8 +2007,15 @@ static void its_free_pending_table(struct page *pt)
 		   get_order(max_t(u32, LPI_PENDBASE_SZ, SZ_64K)));
 }
 
+/*
+ * Booting with kdump and LPIs enabled is generally fine.
+ */
 static bool enabled_lpis_allowed(void)
 {
+	/* Allow a kdump kernel */
+	if (is_kdump_kernel())
+		return true;
+
 	return false;
 }