[PATCH 1/8] x86/platform/UV: Fix panic with missing UVsystab support

[Mike Travis <travis@sgi.com>]

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Fix the panic where KEXEC'd kernel does not have access to EFI runtime
mappings.  This may cause the extended UVsystab to not be available.
The solution is to revert to non-UV mode and continue with limited
capabilities.

Signed-off-by: Mike Travis <travis@sgi.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Reviewed-by: Russ Anderson <rja@hpe.com>
Reviewed-by: Alex Thorlton <athorlton@sgi.com>
---
 arch/x86/kernel/apic/x2apic_uv_x.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

--- linux.orig/arch/x86/kernel/apic/x2apic_uv_x.c
+++ linux/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -1172,19 +1172,25 @@ static void __init decode_gam_rng_tbl(un
 		index, _min_socket, _max_socket, _min_pnode, _max_pnode);
 }
 
-static void __init decode_uv_systab(void)
+static int __init decode_uv_systab(void)
 {
 	struct uv_systab *st;
 	int i;
 
+	if (uv_hub_info->hub_revision < UV4_HUB_REVISION_BASE)
+		return 0;	/* No extended UVsystab required */
+
 	st = uv_systab;
-	if ((!st || st->revision < UV_SYSTAB_VERSION_UV4) && !is_uv4_hub())
-		return;
-	if (st->revision != UV_SYSTAB_VERSION_UV4_LATEST) {
-		pr_crit(
+	if ((!st) || (st->revision < UV_SYSTAB_VERSION_UV4_LATEST)) {
+		int rev = st ? st->revision : 0;
+
+		pr_err(
 		"UV: BIOS UVsystab version(%x) mismatch, expecting(%x)\n",
-			st->revision, UV_SYSTAB_VERSION_UV4_LATEST);
-		BUG();
+			rev, UV_SYSTAB_VERSION_UV4_LATEST);
+		pr_err(
+		"UV: Cannot support UV operations, switching to generic PC\n");
+		uv_system_type = UV_NONE;
+		return -EINVAL;
 	}
 
 	for (i = 0; st->entry[i].type != UV_SYSTAB_TYPE_UNUSED; i++) {
@@ -1205,6 +1211,7 @@ static void __init decode_uv_systab(void
 			break;
 		}
 	}
+	return 0;
 }
 
 /*
@@ -1373,7 +1380,8 @@ void __init uv_system_init(void)
 	map_low_mmrs();
 
 	uv_bios_init();			/* get uv_systab for decoding */
-	decode_uv_systab();
+	if (decode_uv_systab() < 0)
+		return;			/* UVsystab problem, abort UV init */
 	build_socket_tables();
 	build_uv_gr_table();
 	uv_init_hub_info(&hub_info);

--