Re: [Xen-devel] Can't boot as Xen dom0 due to commit fe055896

[Borislav Petkov <bp@xxxxxxx>]

On Fri, Dec 16, 2016 at 11:00:29AM +0100, Juergen Gross wrote:
> Should work. I'm happy to test any patch. :-)

I'm happy that you're happy to! :-)

Let's try this below.

Thanks!

---
diff --git a/arch/x86/kernel/cpu/microcode/core.c 
b/arch/x86/kernel/cpu/microcode/core.c
index 6996413c78c3..c4bb2f7169f6 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -44,7 +44,7 @@
 #define DRIVER_VERSION "2.2"
 
 static struct microcode_ops    *microcode_ops;
-static bool dis_ucode_ldr;
+static bool dis_ucode_ldr = true;
 
 LIST_HEAD(microcode_cache);
 
@@ -76,6 +76,7 @@ struct cpu_info_ctx {
 static bool __init check_loader_disabled_bsp(void)
 {
        static const char *__dis_opt_str = "dis_ucode_ldr";
+       u32 a, b, c, d;
 
 #ifdef CONFIG_X86_32
        const char *cmdline = (const char *)__pa_nodebug(boot_command_line);
@@ -88,8 +89,23 @@ static bool __init check_loader_disabled_bsp(void)
        bool *res = &dis_ucode_ldr;
 #endif
 
-       if (cmdline_find_option_bool(cmdline, option))
-               *res = true;
+       if (!have_cpuid_p())
+               return *res;
+
+       a = 1;
+       c = 0;
+       native_cpuid(&a, &b, &c, &d);
+
+       /*
+        * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
+        * completely accurate as xen pv guests don't see that CPUID bit set but
+        * that's good enough as they don't land on the BSP path anyway.
+        */
+       if (c & BIT(31))
+               return *res;
+
+       if (cmdline_find_option_bool(cmdline, option) <= 0)
+               *res = false;
 
        return *res;
 }
@@ -121,9 +137,6 @@ void __init load_ucode_bsp(void)
        if (check_loader_disabled_bsp())
                return;
 
-       if (!have_cpuid_p())
-               return;
-
        vendor = x86_cpuid_vendor();
        family = x86_cpuid_family();
 
@@ -157,9 +170,6 @@ void load_ucode_ap(void)
        if (check_loader_disabled_ap())
                return;
 
-       if (!have_cpuid_p())
-               return;
-
        vendor = x86_cpuid_vendor();
        family = x86_cpuid_family();
 

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 
(AG Nürnberg)
-- 

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