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lguest: fix crash 'unhandled trap 13 at <native_read_msr_safe>'

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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>
This commit is contained in:
Rusty Russell 2009-03-09 10:06:22 -06:00
parent 7a203f3b08
commit cbd88c8e6f
1 changed files with 5 additions and 0 deletions
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5
arch/x86/lguest/boot.c
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@ -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