[Xen-changelog] [xen staging] x86/boot: enable NMIs after traps init

[patchbot@xxxxxxx]

commit 072e054359a4d4a4f6c3fa09585667472c4f0f1d
Author:     Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
AuthorDate: Tue Oct 23 11:59:12 2018 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Oct 23 12:33:54 2018 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/cpu/common.c | 3 +++
 xen/arch/x86/setup.c      | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 057859ab14..9af2f307ad 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -819,6 +819,9 @@ 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 93b79c7c0c..55a288f332 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -708,6 +708,9 @@ 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 )
     {
         /*
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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