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

commit a18a0f6850d4b286a5ebf02cd5b22fe496b86349 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 08fe6e8a726e5160e51b9c992da765e2fab29348..789648324abba5e496e96e933d3b8bf754e1aaf9 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -559,7 +559,7 @@ 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)