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Re: [Xen-devel] [PATCH] xen: Introduce 'xen_nopv' to disable PV extensions for HVM guests.

On 07/08/2014 02:47 PM, Konrad Rzeszutek Wilk wrote:
On Tue, Jul 08, 2014 at 02:22:48PM -0400, Boris Ostrovsky wrote:
On 07/08/2014 02:48 PM, konrad@xxxxxxxxxx wrote:
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

By default when CONFIG_XEN and CONFIG_XEN_PVHVM kernels are
run, they will enable the PV extensions (drivers, interrupts, timers,
etc) - which is perfect.

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

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
  Documentation/kernel-parameters.txt |    4 ++++
  arch/x86/xen/enlighten.c            |   14 ++++++++++++++
  2 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/Documentation/kernel-parameters.txt 
index c1b9aa8..5dcfa6e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3691,6 +3691,10 @@ bytes respectively. Such letter suffixes can also be 
entirely omitted.
                        Disables the ticketlock slowpath using Xen PV
+       xen_nopv        [X86,XEN]
+                       Disables the PV optimizations forcing the guest to run
+                       as generic HVM guest with no PV drivers.
        xirc2ps_cs=     [NET,PCMCIA]
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index e220197..fec8963 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1930,10 +1930,21 @@ static void __init xen_hvm_guest_init(void)
+static bool off = false;
A more descriptive name would be better.
disable_pv ?


xen_pvoff ?

ignore_xen ?

How about xen_nopv, to be consistent with the boot option.



+static __init int xen_parse_nopv(char *arg)
+       off = true;
+       return 0;
+early_param("xen_nopv", xen_parse_nopv);
  static uint32_t __init xen_hvm_platform(void)
        uint32_t eax, ebx, ecx, edx, base;
+       if (off)
+               return 0;
        if (xen_pv_domain())
                return 0;
@@ -1953,6 +1964,9 @@ static uint32_t __init xen_hvm_platform(void)
  bool xen_hvm_need_lapic(void)
+       if (off)
+               return false;
        if (xen_pv_domain())
                return false;
        if (!xen_hvm_domain())

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