x86, microcode: Don't initialize microcode code on paravirt

Paravirtual guests are not expected to load microcode into processors
and therefore it is not necessary to initialize microcode loading
logic.

In fact, under certain circumstances initializing this logic may cause
the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
macro which does not work in Xen (the code path that leads to this macro
happens during resume when we call mc_bp_resume()->load_ucode_ap()
->check_loader_disabled_ap())

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: http://lkml.kernel.org/r/1417469264-31470-1-git-send-email-boris.ostrovsky@oracle.com
Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 2ce9051174e608381c6a91171e7e3d0d5a6a44ca..ebd232d7de4db26e5b84f9f57a887586fd166ba0 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -557,7 +557,7 @@ static int __init microcode_init(void)
        struct cpuinfo_x86 *c = &cpu_data(0);
        int error;
 
-       if (dis_ucode_ldr)
+       if (paravirt_enabled() || dis_ucode_ldr)
                return 0;
 
        if (c->x86_vendor == X86_VENDOR_INTEL)