irqchip/gic-v3-its: Allow use of LPI tables in reserved memory

If the LPI tables have been reserved with the EFI reservation
mechanism, we assume that these tables are safe to use even
when we find the redistributors to have LPIs enabled at
boot time, meaning that kexec can now work with GICv3.

You're welcome.
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
Tested-by: Lei Zhang <zhang.lei@jp.fujitsu.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

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

@@ -28,6 +28,7 @@
 #include <linux/list.h>
 #include <linux/list_sort.h>
 #include <linux/log2.h>
+#include <linux/memblock.h>
 #include <linux/mm.h>
 #include <linux/msi.h>
 #include <linux/of.h>
@@ -1629,6 +1630,33 @@ static void its_free_prop_table(struct page *prop_page)
 		   get_order(LPI_PROPBASE_SZ));
 }
 
+static bool gic_check_reserved_range(phys_addr_t addr, unsigned long size)
+{
+	phys_addr_t start, end, addr_end;
+	u64 i;
+
+	/*
+	 * We don't bother checking for a kdump kernel as by
+	 * construction, the LPI tables are out of this kernel's
+	 * memory map.
+	 */
+	if (is_kdump_kernel())
+		return true;
+
+	addr_end = addr + size - 1;
+
+	for_each_reserved_mem_region(i, &start, &end) {
+		if (addr >= start && addr_end <= end)
+			return true;
+	}
+
+	/* Not found, not a good sign... */
+	pr_warn("GICv3: Expected reserved range [%pa:%pa], not found\n",
+		&addr, &addr_end);
+	add_taint(TAINT_CRAP, LOCKDEP_STILL_OK);
+	return false;
+}
+
 static int gic_reserve_range(phys_addr_t addr, unsigned long size)
 {
 	if (efi_enabled(EFI_CONFIG_TABLES))
@@ -1976,15 +2004,19 @@ static void its_free_pending_table(struct page *pt)
 }
 
 /*
- * Booting with kdump and LPIs enabled is generally fine.
+ * Booting with kdump and LPIs enabled is generally fine. Any other
+ * case is wrong in the absence of firmware/EFI support.
  */
 static bool enabled_lpis_allowed(void)
 {
-	/* Allow a kdump kernel */
-	if (is_kdump_kernel())
-		return true;
+	phys_addr_t addr;
+	u64 val;
 
-	return false;
+	/* Check whether the property table is in a reserved region */
+	val = gicr_read_propbaser(gic_data_rdist_rd_base() + GICR_PROPBASER);
+	addr = val & GENMASK_ULL(51, 12);
+
+	return gic_check_reserved_range(addr, LPI_PROPBASE_SZ);
 }
 
 static int __init allocate_lpi_tables(void)
@@ -2052,6 +2084,7 @@ static void its_cpu_init_lpis(void)
 		paddr = gicr_read_pendbaser(rbase + GICR_PENDBASER);
 		paddr &= GENMASK_ULL(51, 16);
 
+		WARN_ON(!gic_check_reserved_range(paddr, LPI_PENDBASE_SZ));
 		its_free_pending_table(gic_data_rdist()->pend_page);
 		gic_data_rdist()->pend_page = NULL;