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authorJuergen Gross <jgross@suse.com>2022-09-26 13:16:56 +0200
committerJuergen Gross <jgross@suse.com>2022-10-11 10:51:05 +0200
commit3fac3734c43a2e21fefeb72124d8bd31dff3956f (patch)
treed500099e8e4eb012db4510dfaf17da126f3156df
parenta1886b915e81439ba045b1431f3319d37ac1b906 (diff)
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: Juergen Gross <jgross@suse.com>
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt6
-rw-r--r--arch/x86/xen/Kconfig9
-rw-r--r--arch/x86/xen/enlighten_pv.c24
3 files changed, 29 insertions, 10 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 426fa892d311..1bda9cf18fae 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -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
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 85246dd9faa1..9b1ec5d8c99c 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -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.
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 8c2acccebfe1..0ad3d4bf52b3 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -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 */