x86/boot: enable NMIs after traps init

In certain scenarios, NMIs might be disabled during Xen boot process.
Such situation will cause alternative_instructions() to:

    panic("Timed out waiting for alternatives self-NMI to hit\n");

This bug was originally seen when using Tboot to boot Xen 4.11

To prevent this from happening, enable NMIs during cpu_init() and
during __start_xen() for BSP.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 072e054359a4d4a4f6c3fa09585667472c4f0f1d
master date: 2018-10-23 12:33:54 +0100

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index eb266c5ba64a07819daf1eccbbb03ae8ae3a2ffc..84249be993da928bfea1bb51aabb0241149bb09b 100644 (file)
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -821,6 +821,9 @@ void cpu_init(void)
 #define CD(register) asm volatile ( "mov %0,%%db" #register : : "r"(0UL) );
        CD(0); CD(1); CD(2); CD(3); /* no db4 and db5 */; CD(6); CD(7);
 #undef CD
+
+       /* Enable NMIs.  Our loader (e.g. Tboot) may have left them disabled. */
+       enable_nmis();
 }
 
 void cpu_uninit(unsigned int cpu)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 91520e761215968cc00a67ccf093ffea205e1b0d..617dbb18c9ddcd8e45720a0aa1a5ade377420c30 100644 (file)
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -700,6 +700,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 
     /* Full exception support from here on in. */
 
+    /* Enable NMIs.  Our loader (e.g. Tboot) may have left them disabled. */
+    enable_nmis();
+
     if ( pvh_boot )
     {
         ASSERT(mbi_p == 0);