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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Jul 06, 2015 at 11:34:23PM -0400, Boris Ostrovsky wrote:
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>  arch/x86/xen/enlighten.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 0b95c9b..7953e68 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;
>  
> -		load_percpu_segment(cpu); /* We need to access per-cpu area */
> +		setup_stack_canary_segment(cpu);
>  		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 +1392,16 @@ static void __ref xen_setup_gdt(int cpu)
>  		loadsegment(ds, 0);
>  		loadsegment(fs, 0);
>  #else
> -		/* PVH: TODO Implement. */
> -		BUG();
> +		asm volatile ("ljmp %1,$1f\n"
> +			      "1:\n"
> +			      "movl %2,%0\n"
> +			      "movl %0,%%ss\n"
> +			      "movl %3,%0\n"
> +			      "movl %0,%%ds\n"
> +			      "movl %0,%%es\n"
> +			      : "=&r" (dummy)
> +			      : "i" (__KERNEL_CS), "i" (__KERNEL_DS),
> +				"i" (__USER_DS));
>  #endif

Which comes out to:
ljmp $96,$1f			#[KERNEL_CS]
1:
movl $104,%eax  #, dummy        #[KERNEL_DS] 
movl %eax,%ss   # dummy                                                         
movl $123,%eax  #, dummy         #[USER_DS]                                      
movl %eax,%ds   # dummy                                                         
movl %eax,%es   # dummy    

And that looks right

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

>  		return; /* PVH does not need any PV GDT ops. */
>  	}
> -- 
> 1.8.1.4
>