linux-kernel - Re: [PATCH v3 3/4] Revert "xen: Introduce 'xen_nopv' to disable PV extensions for HVM guests."

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Message-ID: <20190702034818.GB8003@bostrovs-us.us.oracle.com>
Date:   Mon, 1 Jul 2019 23:48:18 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        boris.ostrovsky@...cle.co, jgross@...e.com, sstabellini@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Subject: Re: [PATCH v3 3/4] Revert "xen: Introduce 'xen_nopv' to disable PV
 extensions for HVM guests."

On Mon, Jul 01, 2019 at 10:20:27AM +0800, Zhenzhong Duan wrote:
> This reverts commit 8d693b911bb9c57009c24cb1772d205b84c7985c.
> 
> Instead we use an unified parameter 'nopv' for all the hypervisor
> platforms.
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
> Reviewed-by: Juergen Gross <jgross@...e.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Stefano Stabellini <sstabellini@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  4 ----
>  arch/x86/xen/enlighten_hvm.c                    | 12 +-----------
>  2 files changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 21e08af..d5c3dcc 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5251,10 +5251,6 @@
>  			Disables the ticketlock slowpath using Xen PV
>  			optimizations.
>  
> -	xen_nopv	[X86]
> -			Disables the PV optimizations forcing the HVM guest to
> -			run as generic HVM guest with no PV drivers.
> -


So someone upgrades the kernel and suddenly things work differently?

At least there should be a warning that the option has been replaced
with 'nopv' (but I would actually keep this option working as well).

-boris



>  	xen_scrub_pages=	[XEN]
>  			Boolean option to control scrubbing pages before giving them back
>  			to Xen, for use by other domains. Can be also changed at runtime
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index ac4943c..7fcb4ea 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -210,18 +210,8 @@ static void __init xen_hvm_guest_init(void)
>  #endif
>  }
>  
> -static bool xen_nopv;
> -static __init int xen_parse_nopv(char *arg)
> -{
> -       xen_nopv = true;
> -       return 0;
> -}
> -early_param("xen_nopv", xen_parse_nopv);
> -
>  bool __init xen_hvm_need_lapic(void)
>  {
> -	if (xen_nopv)
> -		return false;
>  	if (xen_pv_domain())
>  		return false;
>  	if (!xen_hvm_domain())
> @@ -233,7 +223,7 @@ bool __init xen_hvm_need_lapic(void)
>  
>  static uint32_t __init xen_platform_hvm(void)
>  {
> -	if (xen_pv_domain() || xen_nopv)
> +	if (xen_pv_domain())
>  		return 0;
>  
>  	return xen_cpuid_base();
> -- 
> 1.8.3.1
>