x86/platform/UV: Fix panic with missing UVsystab support

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>
Reviewed-by: Russ Anderson <rja@hpe.com>
Reviewed-by: Alex Thorlton <athorlton@sgi.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170113152111.118886202@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index 35690a168cf7491d960b34c978a9125bba78c6a0..43930787cab9689b6ff2f3a487309d7ff71a78e7 100644 (file)
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -1172,19 +1172,25 @@ static void __init decode_gam_rng_tbl(unsigned long ptr)
                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);