[xen stable-4.16] xen: arm: Don't use stop_cpu() in halt_this_cpu()

[patchbot@xxxxxxx]

commit 48b67651746f3124b0d5d30147180f1238d2e9c6
Author:     Dmytro Semenets <dmytro_semenets@xxxxxxxx>
AuthorDate: Thu Jun 23 10:44:28 2022 +0300
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Wed Aug 3 14:58:11 2022 -0700

    xen: arm: Don't use stop_cpu() in halt_this_cpu()
    
    When shutting down (or rebooting) the platform, Xen will call stop_cpu()
    on all the CPUs but one. The last CPU will then request the system to
    shutdown/restart.
    
    On platform using PSCI, stop_cpu() will call PSCI CPU off. Per the spec
    (section 5.5.2 DEN0022D.b), the call could return DENIED if the Trusted
    OS is resident on the CPU that is about to be turned off.
    
    As Xen doesn't migrate off the trusted OS (which BTW may not be
    migratable), it would be possible to hit the panic().
    
    In the ideal situation, Xen should migrate the trusted OS or make sure
    the CPU off is not called. However, when shutting down (or rebooting)
    the platform, it is pointless to try to turn off all the CPUs (per
    section 5.10.2, it is only required to put the core in a known state).
    
    So solve the problem by open-coding stop_cpu() in halt_this_cpu() and
    not call PSCI CPU off.
    
    Signed-off-by: Dmytro Semenets <dmytro_semenets@xxxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
    (cherry picked from commit ee11f092b515bf3c926eaad053d12d3f2b6e593e)
---
 xen/arch/arm/shutdown.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/shutdown.c b/xen/arch/arm/shutdown.c
index 3dc6819d56..a9aea19e8e 100644
--- a/xen/arch/arm/shutdown.c
+++ b/xen/arch/arm/shutdown.c
@@ -8,7 +8,12 @@
 
 static void noreturn halt_this_cpu(void *arg)
 {
-    stop_cpu();
+    local_irq_disable();
+    /* Make sure the write happens before we sleep forever */
+    dsb(sy);
+    isb();
+    while ( 1 )
+        wfi();
 }
 
 void machine_halt(void)
--
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