[PATCH 3/6] 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 is already 'xen_nopv' parameter for XEN platform but not for
others. 'xen_nopv' can then be removed with this change.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
---
 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 arch/x86/kernel/cpu/hypervisor.c                | 11 +++++++++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f666..b352f36 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5268,6 +5268,10 @@
 			improve timer resolution at the expense of processing
 			more timer interrupts.
 
+	nopv=		[X86]
+			Disables the PV optimizations forcing the guest to run
+			as generic guest with no PV drivers.
+
 	xirc2ps_cs=	[NET,PCMCIA]
 			Format:
 			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
diff --git a/arch/x86/kernel/cpu/hypervisor.c b/arch/x86/kernel/cpu/hypervisor.c
index 479ca47..4f2c875 100644
--- a/arch/x86/kernel/cpu/hypervisor.c
+++ b/arch/x86/kernel/cpu/hypervisor.c
@@ -85,10 +85,21 @@ static void __init copy_array(const void *src, void *target, unsigned int size)
 			to[i] = from[i];
 }
 
+static bool nopv;
+static __init int xen_parse_nopv(char *arg)
+{
+	nopv = true;
+	return 0;
+}
+early_param("nopv", xen_parse_nopv);
+
 void __init init_hypervisor_platform(void)
 {
 	const struct hypervisor_x86 *h;
 
+	if (nopv)
+		return;
+
 	h = detect_hypervisor_vendor();
 
 	if (!h)
-- 
1.8.3.1