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Re: [PATCH v2 4/4] xen/arm: mpu: Implement a dummy enable_secondary_cpu_mm


  • To: Julien Grall <julien@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Ayan Kumar Halder <ayankuma@xxxxxxx>
  • Date: Tue, 24 Sep 2024 12:34:31 +0100
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  • Delivery-date: Tue, 24 Sep 2024 11:34:47 +0000
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On 19/09/2024 14:20, Julien Grall wrote:
Hi,
Hi Julien,

On 18/09/2024 19:51, Ayan Kumar Halder wrote:
Secondary cpus initialization is not yet supported. Thus, we print an
appropriate message and put the secondary cpus in WFE state.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
---
Changes from :-

v1 - 1. NR_CPUS is defined as 1 for MPU

2. Added a message in enable_secondary_cpu_mm()

  xen/arch/Kconfig              |  1 +
  xen/arch/arm/arm64/mpu/head.S | 10 ++++++++++
  2 files changed, 11 insertions(+)

diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
index 308ce129a8..8640b7ec8b 100644
--- a/xen/arch/Kconfig
+++ b/xen/arch/Kconfig
@@ -11,6 +11,7 @@ config NR_CPUS
      default "8" if ARM && RCAR3
      default "4" if ARM && QEMU
      default "4" if ARM && MPSOC
+    default "1" if ARM && MPU
      default "128" if ARM
      help
        Controls the build-time size of various arrays and bitmaps
diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S
index ef55c8765c..3dfbbf8879 100644
--- a/xen/arch/arm/arm64/mpu/head.S
+++ b/xen/arch/arm/arm64/mpu/head.S
@@ -168,6 +168,16 @@ FUNC(enable_boot_cpu_mm)
      b   1b
  END(enable_boot_cpu_mm)
  +/*
+ * Secondary cpu has not yet been supported on MPU systems. We will block the
+ * secondary cpu bringup at this stage.

Given that NR_CPUS is 1, this should not be reachable. How about the following comment:

"We don't yet support secondary CPUs bring-up. Implement a dummy helper to please the common code."
Ack.

+ */
+ENTRY(enable_secondary_cpu_mm)
+1:  PRINT("- SMP not enabled yet -\r\n")

You want the print to be outside of the loop. Otherwise, it will spam the console in the unlikely case the code is reached.

Ack.

- Ayan


+    wfe
+    b 1b
+ENDPROC(enable_secondary_cpu_mm)
+
  /*
   * Local variables:
   * mode: ASM

Cheers,




 


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