linux-kernel - Re: [PATCH v2 4/6] xen/x86/pvh: Set up descriptors for 32-bit PVH guests

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Message-ID: <20150717152113.GB18085@l.oracle.com>
Date:	Fri, 17 Jul 2015 11:21:13 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	david.vrabel@...rix.com, roger.pau@...rix.com,
	elena.ufimtseva@...cle.com, stefano.stabellini@...citrix.com,
	tim@....org, jbeulich@...e.com, andrew.cooper3@...rix.com,
	ian.campbell@...rix.com, ian.jackson@...citrix.com,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] xen/x86/pvh: Set up descriptors for 32-bit PVH
 guests

On Thu, Jul 16, 2015 at 05:43:39PM -0400, Boris Ostrovsky wrote:
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
> Changes in v2:
> * Set segment selectors using loadsegment() instead of assembly
> 
>  arch/x86/xen/enlighten.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index f8dc398..d665b1d 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1362,12 +1362,12 @@ static void __init xen_boot_params_init_edd(void)
>  static void __ref xen_setup_gdt(int cpu)
>  {
>  	if (xen_feature(XENFEAT_auto_translated_physmap)) {
> -#ifdef CONFIG_X86_64
> -		unsigned long dummy;
> +		unsigned long __attribute__((unused)) dummy;
>  
> -		load_percpu_segment(cpu); /* We need to access per-cpu area */

You removed that - where are we going to do that? As the
'switch_to_new_gdt' uses the per-cpu GDT table.

> +		setup_stack_canary_segment(cpu);

As this one too ?
>  		switch_to_new_gdt(cpu); /* GDT and GS set */
>  
> +#ifdef CONFIG_X86_64
>  		/* We are switching of the Xen provided GDT to our HVM mode
>  		 * GDT. The new GDT has  __KERNEL_CS with CS.L = 1
>  		 * and we are jumping to reload it.
> @@ -1392,8 +1392,13 @@ static void __ref xen_setup_gdt(int cpu)
>  		loadsegment(ds, 0);
>  		loadsegment(fs, 0);
>  #else
> -		/* PVH: TODO Implement. */
> -		BUG();
> +		asm volatile ("ljmp %0,$1f\n"
> +			      "1:\n"
> +			      :: "i" (__KERNEL_CS));
> +
> +		loadsegment(ss, __KERNEL_DS);
> +		loadsegment(ds, __USER_DS);
> +		loadsegment(es, __USER_DS);
>  #endif
>  		return; /* PVH does not need any PV GDT ops. */
>  	}
> -- 
> 1.8.1.4
> 
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