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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

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@kernel.org wrote:
>>> From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>
>>> 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@oracle.com>
>>> ---
>>>   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 b/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
>>>   			optimizations.
>>> +	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]
>>>   			Format:
>>>   			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
>>> 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)
>>>   #endif
>>>   }
>>> +static bool off = false;
>> A more descriptive name would be better.
> disable_pv ?
>
> disable?
>
> xen_pvoff ?
>
> ignore_xen ?

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

-boris


>
>
>> -boris
>>
>>> +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())