Re: [kvmarm] [PATCH v10 06/14] KVM: ARM: Hypervisor inititalization

[Marc Zyngier <marc.zyngier@arm.com>]

On Fri, 24 Aug 2012 16:04:02 +0800, Lei Wen <adrian.wenl@gmail.com> wrote:
> On Thu, Aug 23, 2012 at 11:27 PM, Christoffer Dall
> <c.dall@virtualopensystems.com> wrote:
>> On Thu, Aug 23, 2012 at 11:08 AM, Lei Wen <adrian.wenl@gmail.com>
wrote:
>>> Hi Christoffer,
>>>
>>> [snip]
>>>
>>>> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
>>>> index 1dc8926..4db26cb 100644
>>>> --- a/arch/arm/kvm/init.S
>>>> +++ b/arch/arm/kvm/init.S
>>>> @@ -15,5 +15,135 @@
>>>>   * along with this program; if not, write to the Free Software
>>>>   * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 
>>>>   02110-1301, USA.
>>>>   */
>>>> +
>>>> +#include <linux/linkage.h>
>>>> +#include <asm/unified.h>
>>>>  #include <asm/asm-offsets.h>
>>>>  #include <asm/kvm_asm.h>
>>>> +#include <asm/kvm_arm.h>
>>>> +
>>>>
+@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
>>>> +@  Hypervisor initialization
>>>> +@    - should be called with:
>>>> +@        r0 = Hypervisor pgd pointer
>>>> +@        r1 = top of Hyp stack (kernel VA)
>>>>
+@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
>>>> +       .text
>>>> +       .arm
>>>> +        .pushsection    .hyp.idmap.text,"ax"
>>>> +       .align 12
>>>> +__kvm_hyp_init:
>>>> +       .globl __kvm_hyp_init
>>>> +
>>>> +       @ Hyp-mode exception vector
>>>> +       nop
>>>> +       nop
>>>> +       nop
>>>> +       nop
>>>> +       nop
>>>> +       b       __do_hyp_init
>>>> +       nop
>>>> +       nop
>>>> +
>>>> +__do_hyp_init:
>>>> +       @ Set the sp to end of this page and push data for later use
>>>> +       mov     sp, pc
>>>> +       bic     sp, sp, #0x0ff
>>>> +       bic     sp, sp, #0xf00
>>>> +       add     sp, sp, #0x1000
>>>> +       push    {r0, r1, r2, r12}
>>>
>>> Is safe to use the stack here? Since our HYP memory mapping is
>>> gotten valid after the following HTTBR being set as I think.
>>>
>>
>> yes, as you can see in the end of this block we have a .align 12
>> before __kvm_hyp_init_end giving us the stack space we need in this
>> page (as long as this init code doesn't grow beyond ~3K
> 
> I know this area is already being mapped in hyp_init_static_idmap,
> however, due to the HTTBR is not being set up yet in the below code.
> So how the memory get mapped in the hyp mode? I mean what I could
> understand the hyp virtual address only could be seen after HTTBR
> being set up.

Hint: look at HSCTLR, and when the M bit gets set. Until then, the words
"virtual address" have no meaning.

        M.
-- 
Fast, cheap, reliable. Pick two.