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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Jul 06, 2015 at 11:34:23PM -0400, Boris Ostrovsky wrote:
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

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

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