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Commit 82d64699 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge
Browse files

xen: mask extended topology info in cpuid 



A Xen guest never needs to know about extended topology, and knowing
would just confuse it.

This patch just zeros ebx in leaf 0xb which indicates no topology info,
preventing a crash under Xen on cpus which support this leaf.

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>
parent 7825cf10

arch/x86/xen/enlighten.c

+10 −1
Original line number Diff line number Diff line
@@ -178,6 +178,7 @@ static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0; 
static void xen_cpuid(unsigned int *ax, unsigned int *bx,

		      unsigned int *cx, unsigned int *dx)

{

	unsigned maskebx = ~0;

	unsigned maskecx = ~0;

	unsigned maskedx = ~0;
@@ -185,9 +186,16 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx, 
	 * Mask out inconvenient features, to try and disable as many

	 * unsupported kernel subsystems as possible.

	 */

	if (*ax == 1) {

	switch (*ax) {

	case 1:

		maskecx = cpuid_leaf1_ecx_mask;

		maskedx = cpuid_leaf1_edx_mask;

		break;



	case 0xb:

		/* Suppress extended topology stuff */

		maskebx = 0;

		break;

	}



	asm(XEN_EMULATE_PREFIX "cpuid"
@@ -197,6 +205,7 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx, 
		  "=d" (*dx)

		: "0" (*ax), "2" (*cx));



	*bx &= maskebx;

	*cx &= maskecx;

	*dx &= maskedx;

}