Commit 3fac3734 authored by Juergen Gross's avatar Juergen Gross
Browse files

xen/pv: support selecting safe/unsafe msr accesses 



Instead of always doing the safe variants for reading and writing MSRs
in Xen PV guests, make the behavior controllable via Kconfig option
and a boot parameter.

The default will be the current behavior, which is to always use the
safe variant.

Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent a1886b91

Documentation/admin-guide/kernel-parameters.txt

+6 −0
Original line number Diff line number Diff line
@@ -6836,6 +6836,12 @@ 
			Crash from Xen panic notifier, without executing late

			panic() code such as dumping handler.



	xen_msr_safe=	[X86,XEN]

			Format: <bool>

			Select whether to always use non-faulting (safe) MSR

			access functions when running as Xen PV guest. The

			default value is controlled by CONFIG_XEN_PV_MSR_SAFE.



	xen_nopvspin	[X86,XEN]

			Disables the qspinlock slowpath using Xen PV optimizations.

			This parameter is obsoleted by "nopvspin" parameter, which

arch/x86/xen/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -92,3 +92,12 @@ config XEN_DOM0 
	select X86_X2APIC if XEN_PVH && X86_64

	help

	  Support running as a Xen Dom0 guest.



config XEN_PV_MSR_SAFE

	bool "Always use safe MSR accesses in PV guests"

	default y

	depends on XEN_PV

	help

	  Use safe (not faulting) MSR access functions even if the MSR access

	  should not fault anyway.

	  The default can be changed by using the "xen_msr_safe" boot parameter.

arch/x86/xen/enlighten_pv.c

+14 −10
Original line number Diff line number Diff line
@@ -108,6 +108,16 @@ struct tls_descs { 
 */

static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);



static __read_mostly bool xen_msr_safe = IS_ENABLED(CONFIG_XEN_PV_MSR_SAFE);



static int __init parse_xen_msr_safe(char *str)

{

	if (str)

		return strtobool(str, &xen_msr_safe);

	return -EINVAL;

}

early_param("xen_msr_safe", parse_xen_msr_safe);



static void __init xen_pv_init_platform(void)

{

	/* PV guests can't operate virtio devices without grants. */
@@ -1010,22 +1020,16 @@ static int xen_write_msr_safe(unsigned int msr, unsigned int low, 


static u64 xen_read_msr(unsigned int msr)

{

	/*

	 * This will silently swallow a #GP from RDMSR.  It may be worth

	 * changing that.

	 */

	int err;



	return xen_read_msr_safe(msr, &err);

	return xen_do_read_msr(msr, xen_msr_safe ? &err : NULL);

}



static void xen_write_msr(unsigned int msr, unsigned low, unsigned high)

{

	/*

	 * This will silently swallow a #GP from WRMSR.  It may be worth

	 * changing that.

	 */

	xen_write_msr_safe(msr, low, high);

	int err;



	xen_do_write_msr(msr, low, high, xen_msr_safe ? &err : NULL);

}



/* This is called once we have the cpu_possible_mask */