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xen/pv: support selecting safe/unsafe msr accesses

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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: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2022-09-26 13:16:56 +02:00
parent a1886b915e
commit 3fac3734c4
3 changed files with 29 additions and 10 deletions
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6
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

9
arch/x86/xen/Kconfig
View File

@ -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.

24
arch/x86/xen/enlighten_pv.c
View File

@ -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 */