On Fri, Sep 18, 2015 at 12:04 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Sep 18, 2015 at 08:20:46AM -0700, Andy Lutomirski wrote:
>> In any event, Borislav, you must have typed rdmsr_safe for a reason :)
>
> Wasn't me:
>
> 6c62aa4a3c12 ("x86: make amd.c have 64bit support code")
>
> I think the error handling of rdmsrl_safe() was needed to do the pfn
> games which are done in the if-clause.
I just tried it. rdmsrl_safe and friends definitely work fine in that
code. I think that Linux's Xen startup code is buggy and fails to set
up early exception handling.
Try this (horribly whitespace damaged):
static void __init early_identify_cpu(struct cpuinfo_x86 *c)
{
+ u64 tmp;
#ifdef CONFIG_X86_64
c->x86_clflush_size = 64;
c->x86_phys_bits = 36;
@@ -752,6 +753,9 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
c->cpu_index = 0;
filter_cpuid_features(c, false);
+ pr_err("trying to crash\n");
+ rdmsrl_safe(0x12345678, &tmp);
+
It works fine. I bet it crashes on a Xen guest, though. I assume
that Xen just works in most cases by luck.
--Andy
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