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

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Message-Id: <201407112331.s6BNVp9C022670@aserz7021.oracle.com>
Date:	Fri, 11 Jul 2014 19:31:31 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	konrad@...nel.org, xen-devel@...ts.xenproject.org,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: Introduce 'xen_nopv' to disable PV extensions for
 HVM guests.


On Jul 11, 2014 7:14 PM, "H. Peter Anvin" <hpa@...or.com> wrote:
>
> On 07/11/2014 04:09 PM, Konrad Rzeszutek Wilk wrote: 
> > 
> > On Jul 11, 2014 6:52 PM, "H. Peter Anvin" <hpa@...or.com> wrote: 
> >> 
> >> On 07/11/2014 12:53 PM, konrad@...nel.org wrote: 
> >>> 
> >>> 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 ffb101e..eb82239 100644 
> >>> --- a/arch/x86/xen/enlighten.c 
> >>> +++ b/arch/x86/xen/enlighten.c 
> >>> @@ -1826,8 +1826,19 @@ static void __init xen_hvm_guest_init(void) 
> >>>   xen_hvm_init_mmu_ops(); 
> >>>   } 
> >>>   
> >>> +static bool xen_nopv = false; 
> >>> +static __init int xen_parse_nopv(char *arg) 
> >>> +{ 
> >>> +       xen_nopv = true; 
> >>> +       return 0; 
> >>> +} 
> >>> +early_param("xen_nopv", xen_parse_nopv); 
> >>> + 
> >>>   static uint32_t __init xen_hvm_platform(void) 
> >>>   { 
> >>> + if (xen_nopv) 
> >>> + return 0; 
> >>> + 
> >>>   if (xen_pv_domain()) 
> >>>   return 0; 
> >>>   
> >>> @@ -1836,6 +1847,8 @@ static uint32_t __init xen_hvm_platform(void) 
> >>>   
> >>>   bool xen_hvm_need_lapic(void) 
> >>>   { 
> >>> + if (xen_nopv) 
> >>> + return false; 
> >>>   if (xen_pv_domain()) 
> >>>   return false; 
> >>>   if (!xen_hvm_domain()) 
> >>> 
> >> 
> >> Any reason to not simply let xen_pv_domain() return false here? 
> > 
> > It does return false already. 
> > 
> > Did you mean to collapse them together? 
>
> OK, I'm confused.  The description of the option makes it look like it 
> could disable things associated with PV domains, but it looks like it 
> actually disables things having to do with HVM domains... 
>

Thank you for pointing that out. I will update the documentation to be more clear and specific. It is as you surmised only for HVM guest.

The a
> -hpa 
>