Commit cbd88c8e authored Mar 09, 2009 by Rusty Russell

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>

parent 7a203f3b

arch/x86/lguest/boot.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -343,6 +343,11 @@ static void lguest_cpuid(unsigned int ax, unsigned int bx,
		* 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

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