linux-kernel - Re: [PATCH] pvh: set cr4 flags for APs

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Date:	Mon, 3 Feb 2014 12:51:29 -0800
From:	Mukesh Rathor <mukesh.rathor@...cle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	roger.pau@...rix.com, Xen-devel@...ts.xensource.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pvh: set cr4 flags for APs

On Mon, 3 Feb 2014 15:43:46 -0500
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:

> On Mon, Feb 03, 2014 at 02:52:40PM -0500, Konrad Rzeszutek Wilk wrote:
> > On Mon, Feb 03, 2014 at 11:30:01AM -0800, Mukesh Rathor wrote:
> > > On Mon, 3 Feb 2014 06:49:14 -0500
> > > Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> > > 
> > > > On Wed, Jan 29, 2014 at 04:15:18PM -0800, Mukesh Rathor wrote:
> > > > > We need to set cr4 flags for APs that are already set for BSP.
> > > > 
> > > > The title is missing the 'xen' part.
> > > 
> > > The patch is for linux, not xen.
> > 
> > Right. And hence you need to prefix the title with 'xen' in it
> > otherwise it won't be obvious from the Linux log line for what
> > component of the Linux tree it is.
> > 
> > > 
> > > > I rewrote it a bit and I think this should go in 3.14.
> > > > 
> > > > David, Boris: It is not the full fix as there are other parts to
> > > > make an PVH guest use 2MB or 1GB pages- but this fixes an
> > > > obvious bug.
> > > > 
> > > > 
> > > > 
> > > > From 797ea6812ff0a90cce966a4ff6bad57cbadc43b5 Mon Sep 17
> > > > 00:00:00 2001 From: Mukesh Rathor <mukesh.rathor@...cle.com>
> > > > Date: Wed, 29 Jan 2014 16:15:18 -0800
> > > > Subject: [PATCH] xen/pvh: set CR4 flags for APs
> > > > 
> > > > The Xen ABI sets said flags for the BSP, but it does
> > > 
> > > NO it does not. I said it few times, it's set by
> > > probe_page_size_mask (which is in linux) for the BSP. The comment
> > > below also says it.
> > 
> > Where does it set it for APs? Can we piggyback on that?
> 
> And since I am in a hurry to fix an build regression I did the
> research myself - but this kind of information needs to be in the
> commit message.
> 
> Here is what I have, please comment as I want to send a git pull to
> Linux within the hour.
> 
> From 125ef07fd58e963cc286554f6536e46c9712033c Mon Sep 17 00:00:00 2001
> From: Mukesh Rathor <mukesh.rathor@...cle.com>
> Date: Wed, 29 Jan 2014 16:15:18 -0800
> Subject: [PATCH] xen/pvh: set CR4 flags for APs
> 
> During bootup in the 'probe_page_size_mask' these CR4
> flags are set in there. But for AP processors they
> are not set as we do not use 'secondary_startup_64' which
> the baremetal kernels uses. Instead do it in
> this function which we use in Xen PVH during our
> startup for AP and BSP processors.
> 
> As such fix it up to make sure we have that flag set.

Thats good enough for me.

Mukesh


> Signed-off-by: Mukesh Rathor <mukesh.rathor@...cle.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/enlighten.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index a4d7b64..201d09a 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1473,6 +1473,18 @@ static void xen_pvh_set_cr_flags(int cpu)
>  	 * X86_CR0_TS, X86_CR0_PE, X86_CR0_ET are set by Xen for HVM
> guests
>  	 * (which PVH shared codepaths), while X86_CR0_PG is for
> PVH. */ write_cr0(read_cr0() | X86_CR0_MP | X86_CR0_NE | X86_CR0_WP |
> X86_CR0_AM); +
> +	if (!cpu)
> +		return;
> +	/*
> +	 * For BSP, PSE PGE are set in probe_page_size_mask(), for
> APs
> +	 * set them here. For all, OSFXSR OSXMMEXCPT are set in
> fpu_init.
> +	*/
> +	if (cpu_has_pse)
> +		set_in_cr4(X86_CR4_PSE);
> +
> +	if (cpu_has_pge)
> +		set_in_cr4(X86_CR4_PGE);
>  }
>  
>  /*

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