lguest: fix crash 'unhandled trap 13 at <native_read_msr_safe>'
Impact: fix lguest boot crash on modern Intel machines
The code in early_init_intel does:
if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
u64 misc_enable;
rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
And that rdmsr faults (not allowed from non-0 PL). We can get around
this by mugging the family ID part of the cpuid. 5 seems like a good
number.
Of course, this is a hack (how very lguest!). We could just indicate
that we don't support MSRs, or implement lguest_rdmst.
Reported-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Tested-by: Patrick McHardy <kaber@trash.net>
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 92f1c6f..ba5c05e 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -343,6 +343,11 @@
* flush_tlb_user() for both user and kernel mappings unless
* the Page Global Enable (PGE) feature bit is set. */
*dx |= 0x00002000;
+ /* We also lie, and say we're family id 5. 6 or greater
+ * leads to a rdmsr in early_init_intel which we can't handle.
+ * Family ID is returned as bits 8-12 in ax. */
+ *ax &= 0xFFFFF0FF;
+ *ax |= 0x00000500;
break;
case 0x80000000:
/* Futureproof this a little: if they ask how much extended