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Re: [Xen-devel] [PATCH 08/18] xen/arm: Disable/enable non-boot physical CPUs on suspend/resume


On 13/11/2018 22:35, Stefano Stabellini wrote:
On Mon, 12 Nov 2018, Mirela Simonovic wrote:
Non-boot CPUs have to be disabled on suspend and enabled on resume
(hotplug-based mechanism). Disabling non-boot CPUs will lead to PSCI
CPU_OFF to be called by each non-boot CPU. Depending on the underlying
platform capabilities, this may lead to the physical powering down of
CPUs. Tested on Xilinx Zynq Ultrascale+ MPSoC (including power down of
each non-boot CPU).

Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
Signed-off-by: Saeed Nowshadi <saeed.nowshadi@xxxxxxxxxx>
  xen/arch/arm/suspend.c | 15 ++++++++++++++-
  1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/suspend.c b/xen/arch/arm/suspend.c
index 575afd5eb8..dae1b1f7d6 100644
--- a/xen/arch/arm/suspend.c
+++ b/xen/arch/arm/suspend.c
@@ -1,4 +1,5 @@
  #include <xen/sched.h>
+#include <xen/cpu.h>
  #include <asm/cpufeature.h>
  #include <asm/event.h>
  #include <asm/psci.h>
@@ -115,17 +116,29 @@ static void vcpu_suspend(register_t epoint, register_t 
  /* Xen suspend. Note: data is not used (suspend is the suspend to RAM) */
  static long system_suspend(void *data)
+    int status;
      BUG_ON(system_state != SYS_STATE_active);
system_state = SYS_STATE_suspend;
+ status = disable_nonboot_cpus();
+    if ( status )
+    {
+        system_state = SYS_STATE_resume;
+        goto resume_nonboot_cpus;
+    }
      system_state = SYS_STATE_resume;
+    enable_nonboot_cpus();
      system_state = SYS_STATE_active;
+    dsb(sy);
- return -ENOSYS;
+    return status;

I think we need a spin_lock to protect system_suspend from concurrent
calls, or (better) we need to make sure that the caller is only allowed
to call system_suspend if there is just one vcpu active in the system,
and that vcpu is blocked on this PSCI system suspend call.

I don't think this is correct. It is valid to have more than on vCPU running when calling system_suspend. An example would be Dom0 suspending while the other domain are still running.

This is handled properly via freeze_domains()/thaw_domains().

So a spinlock would be a better solution here. If we can't acquire the lock then the function would return -EBUSY.


Julien Grall

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