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

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

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.

-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())