linux-kernel - Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

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Message-ID: <20140715153801.GX3403@laptop.dumpdata.com>
Date:	Tue, 15 Jul 2014 11:38:01 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>, boris.ostrovsky@...cle.com,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
> Xen doesn't call start_secondary.

Duh!
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
> 
> espfix still doesn't seem to work on Xen (it goes boom in some way that
> I don't understand right now), but initializing all CPUs instead of just
> one of them seems like a good start.
> 
> ISTM the right fix is probably to shove the espfix logic into
> native_iret and to tweak the paravirt logic so that native_iret always
> gets invoked.  I suspect that Xen will need its own implementation of
> espfix64 in the hypervisor and that, ultimately, someone may want to
> stop initializing espfix64 at all on Xen guests.

I think just disallowing would be preferrable.

Thanks for posting this patch!
> 
>  arch/x86/xen/smp.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 7005974..eea9bcc 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -23,6 +23,7 @@
>  #include <asm/desc.h>
>  #include <asm/pgtable.h>
>  #include <asm/cpu.h>
> +#include <asm/espfix.h>
>  
>  #include <xen/interface/xen.h>
>  #include <xen/interface/vcpu.h>
> @@ -85,6 +86,13 @@ static void cpu_bringup(void)
>  
>  	xen_setup_cpu_clockevents();
>  
> +	/*
> +	 * Enable the espfix hack for this CPU
> +	 */
> +#ifdef CONFIG_X86_ESPFIX64
> +	init_espfix_ap();
> +#endif
> +
>  	notify_cpu_starting(cpu);
>  
>  	set_cpu_online(cpu, true);
> -- 
> 1.9.3
> 
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