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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 07/07/2015 03:54 PM, Konrad Rzeszutek Wilk wrote:
> 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

Actually, now that look at this again I think I should just use 
loadsegment(), just like 64-bit code above.

-boris


>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>
>>   		return; /* PVH does not need any PV GDT ops. */
>>   	}
>> -- 
>> 1.8.1.4
>>