[PATCH v4 2/5] x86: Add nopv parameter to disable PV extensions

[Zhenzhong Duan]

In virtualization environment, PV extensions (drivers, interrupts,
timers, etc) are enabled in the majority of use cases which is the
best option.

However, in some cases (kexec not fully working, benchmarking)
we want to disable PV extensions. As such introduce the
'nopv' parameter that will do it.

There are guest types which just won't work without PV extensions,
like Xen PV, Xen PVH and jailhouse. add a "ignore_nopv" member to
struct hypervisor_x86 set to true for those guest types and call
the detect functions only if nopv is false or ignore_nopv is true.

There is already 'xen_nopv' parameter for XEN platform but not for
others. 'xen_nopv' can then be removed with this change.

Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 +++++
 arch/x86/include/asm/hypervisor.h               |  3 +++
 arch/x86/kernel/cpu/hypervisor.c                | 11 +++++++++++
 arch/x86/kernel/jailhouse.c                     |  1 +
 arch/x86/xen/enlighten_pv.c                     |  1 +
 5 files changed, 21 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f666..21e08af 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5268,6 +5268,11 @@
 			improve timer resolution at the expense of processing
 			more timer interrupts.
 
+	nopv=		[X86,XEN,KVM,HYPER_V,VMWARE]
+			Disables the PV optimizations forcing the guest to run
+			as generic guest with no PV drivers. Currently support
+			XEN HVM, KVM, HYPER_V and VMWARE guest.
+
 	xirc2ps_cs=	[NET,PCMCIA]
 			Format:
 			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
index 8c5aaba..d75d2ea 100644
--- a/arch/x86/include/asm/hypervisor.h
+++ b/arch/x86/include/asm/hypervisor.h
@@ -52,6 +52,9 @@ struct hypervisor_x86 {
 
 	/* runtime callbacks */
 	struct x86_hyper_runtime runtime;
+
+	/* ignore nopv parameter */
+	bool ignore_nopv;
 };
 
 extern enum x86_hypervisor_type x86_hyper_type;
diff --git a/arch/x86/kernel/cpu/hypervisor.c b/arch/x86/kernel/cpu/hypervisor.c
index 479ca47..337ff07 100644
--- a/arch/x86/kernel/cpu/hypervisor.c
+++ b/arch/x86/kernel/cpu/hypervisor.c
@@ -54,6 +54,14 @@
 enum x86_hypervisor_type x86_hyper_type;
 EXPORT_SYMBOL(x86_hyper_type);
 
+bool __initdata nopv;
+static __init int parse_nopv(char *arg)
+{
+	nopv = true;
+	return 0;
+}
+early_param("nopv", parse_nopv);
+
 static inline const struct hypervisor_x86 * __init
 detect_hypervisor_vendor(void)
 {
@@ -61,6 +69,9 @@
 	uint32_t pri, max_pri = 0;
 
 	for (p = hypervisors; p < hypervisors + ARRAY_SIZE(hypervisors); p++) {
+		if (unlikely(nopv) && !(*p)->ignore_nopv)
+			continue;
+
 		pri = (*p)->detect();
 		if (pri > max_pri) {
 			max_pri = pri;
diff --git a/arch/x86/kernel/jailhouse.c b/arch/x86/kernel/jailhouse.c
index d96d563..880329f 100644
--- a/arch/x86/kernel/jailhouse.c
+++ b/arch/x86/kernel/jailhouse.c
@@ -217,4 +217,5 @@ static bool __init jailhouse_x2apic_available(void)
 	.detect			= jailhouse_detect,
 	.init.init_platform	= jailhouse_init_platform,
 	.init.x2apic_available	= jailhouse_x2apic_available,
+	.ignore_nopv		= true,
 };
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4722ba2..5d16824 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1463,4 +1463,5 @@ static uint32_t __init xen_platform_pv(void)
 	.detect                 = xen_platform_pv,
 	.type			= X86_HYPER_XEN_PV,
 	.runtime.pin_vcpu       = xen_pin_vcpu,
+	.ignore_nopv		= true,
 };
-- 
1.8.3.1