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SubjectRe: Can't boot as Xen dom0 due to commit fe055896
On Fri, Dec 16, 2016 at 08:28:46AM +0100, Juergen Gross wrote:
> Not trying to load ucode in _any_ guest is an optimization only.

Does the hunk below work too?

I don't want to do hypervisor-specific solutions.

---
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 6996413c78c3..54219f619205 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -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);
@@ -91,6 +92,17 @@ static bool __init check_loader_disabled_bsp(void)
if (cmdline_find_option_bool(cmdline, option))
*res = true;

+ if (!have_cpuid_p())
+ *res = true;
+
+ a = 1;
+ c = 0;
+ native_cpuid(&a, &b, &c, &d);
+
+ /* CPUID(1).ECX[31]: reserved for hypervisor use */
+ if (c & BIT(31))
+ *res = true;
+
return *res;
}

@@ -121,9 +133,6 @@ 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 +166,6 @@ 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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