[kvm-unit-tests GIT PULL 04/11] lib/s390x: fix SMP setup bug

[Janosch Frank <frankja@linux.ibm.com>]

From: Claudio Imbrenda <imbrenda@linux.ibm.com>

The lowcore pointer pointing to the current CPU (THIS_CPU) was not
initialized for the boot CPU. The pointer is needed for correct
interrupt handling, which is needed in the setup process before the
struct cpu array is allocated.

The bug went unnoticed because some environments (like qemu/KVM) clear
all memory and don't write anything in the lowcore area before starting
the payload. The pointer thus pointed to 0, an area of memory also not
used. Other environments will write to memory before starting the
payload, causing the unit tests to crash at the first interrupt.

Fix by assigning a temporary struct cpu before the rest of the setup
process, and assigning the pointer to the correct allocated struct
during smp initialization.

Fixes: 4e5dd758 ("lib: s390x: better smp interrupt checks")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Tested-by: Nico Boehr <nrb@linux.ibm.com>
Reported-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20220818152114.213135-1-imbrenda@linux.ibm.com
Message-Id: <20220818152114.213135-1-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 lib/s390x/io.c  | 9 +++++++++
 lib/s390x/smp.c | 1 +
 2 files changed, 10 insertions(+)

diff --git a/lib/s390x/io.c b/lib/s390x/io.c
index a4f1b113..fb7b7dda 100644
--- a/lib/s390x/io.c
+++ b/lib/s390x/io.c
@@ -33,6 +33,15 @@ void puts(const char *s)
 
 void setup(void)
 {
+	struct cpu this_cpu_tmp = { 0 };
+
+	/*
+	 * Set a temporary empty struct cpu for the boot CPU, needed for
+	 * correct interrupt handling in the setup process.
+	 * smp_setup will allocate and set the permanent one.
+	 */
+	THIS_CPU = &this_cpu_tmp;
+
 	setup_args_progname(ipl_args);
 	setup_facilities();
 	sclp_read_info();
diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
index 0d98c17d..03d6d2a4 100644
--- a/lib/s390x/smp.c
+++ b/lib/s390x/smp.c
@@ -353,6 +353,7 @@ void smp_setup(void)
 			cpus[0].stack = stackptr;
 			cpus[0].lowcore = (void *)0;
 			cpus[0].active = true;
+			THIS_CPU = &cpus[0];
 		}
 	}
 	spin_unlock(&lock);
-- 
2.34.1