[Xen-devel,v3,14/28] xen/arm32: head: Rework and document check_cpu_mode()

Message ID 20190812173019.11956-15-julien.grall@arm.com
State New
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Series
  • xen/arm: Rework head.S to make it more compliant with the Arm Arm
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Commit Message

Julien Grall Aug. 12, 2019, 5:30 p.m.
A branch in the success case can be avoided by inverting the branch
condition. At the same time, remove a pointless comment as Xen can only
run at Hypervisor Mode.

Lastly, document the behavior and the main registers usage within the
function.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---
    Changes in v2:
        - Patch added
---
 xen/arch/arm/arm32/head.S | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

Comments

Stefano Stabellini Aug. 22, 2019, 5:14 p.m. | #1
On Mon, 12 Aug 2019, Julien Grall wrote:
> A branch in the success case can be avoided by inverting the branch
> condition. At the same time, remove a pointless comment as Xen can only
> run at Hypervisor Mode.
> 
> Lastly, document the behavior and the main registers usage within the
> function.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Already provided by reviewed-by last time

> ---
>     Changes in v2:
>         - Patch added
> ---
>  xen/arch/arm/arm32/head.S | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 4285f76463..c7b4fe4cd4 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -206,6 +206,16 @@ secondary_switched:
>          b     launch
>  ENDPROC(init_secondary)
>  
> +/*
> + * Check if the CPU supports virtualization extensions and has been booted
> + * in Hypervisor mode.
> + *
> + * This function will never return when the CPU doesn't support
> + * virtualization extensions or is booted in another mode than
> + * Hypervisor mode.
> + *
> + * Clobbers r0 - r3
> + */
>  check_cpu_mode:
>          /* Check that this CPU has Hyp mode */
>          mrc   CP32(r0, ID_PFR1)
> @@ -220,15 +230,12 @@ check_cpu_mode:
>          mrs   r0, cpsr
>          and   r0, r0, #0x1f          /* Mode is in the low 5 bits of CPSR */
>          teq   r0, #0x1a              /* Hyp Mode? */
> -        beq   hyp
> +        moveq pc, lr                 /* Yes, return */
>  
>          /* OK, we're boned. */
>          PRINT("- Xen must be entered in NS Hyp mode -\r\n")
>          PRINT("- Please update the bootloader -\r\n")
>          b     fail
> -
> -hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
> -        mov   pc, lr
>  ENDPROC(check_cpu_mode)
>  
>  zero_bss:
> -- 
> 2.11.0
>
Julien Grall Sept. 7, 2019, 10:35 a.m. | #2
Hi Stefano,

On 8/22/19 6:14 PM, Stefano Stabellini wrote:
> On Mon, 12 Aug 2019, Julien Grall wrote:
>> A branch in the success case can be avoided by inverting the branch
>> condition. At the same time, remove a pointless comment as Xen can only
>> run at Hypervisor Mode.
>>
>> Lastly, document the behavior and the main registers usage within the
>> function.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
> 
> Already provided by reviewed-by last time

Whoops, I will add it in the next revision.

Cheers,

Patch

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 4285f76463..c7b4fe4cd4 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -206,6 +206,16 @@  secondary_switched:
         b     launch
 ENDPROC(init_secondary)
 
+/*
+ * Check if the CPU supports virtualization extensions and has been booted
+ * in Hypervisor mode.
+ *
+ * This function will never return when the CPU doesn't support
+ * virtualization extensions or is booted in another mode than
+ * Hypervisor mode.
+ *
+ * Clobbers r0 - r3
+ */
 check_cpu_mode:
         /* Check that this CPU has Hyp mode */
         mrc   CP32(r0, ID_PFR1)
@@ -220,15 +230,12 @@  check_cpu_mode:
         mrs   r0, cpsr
         and   r0, r0, #0x1f          /* Mode is in the low 5 bits of CPSR */
         teq   r0, #0x1a              /* Hyp Mode? */
-        beq   hyp
+        moveq pc, lr                 /* Yes, return */
 
         /* OK, we're boned. */
         PRINT("- Xen must be entered in NS Hyp mode -\r\n")
         PRINT("- Please update the bootloader -\r\n")
         b     fail
-
-hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
-        mov   pc, lr
 ENDPROC(check_cpu_mode)
 
 zero_bss: