On 8/19/22 11:12, Claudio Imbrenda wrote:
On Fri, 19 Aug 2022 10:52:40 +0200
Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
On 8/18/22 17:21, Claudio Imbrenda wrote:
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@xxxxxxxxxxxxx>
I've considered letting the IPL cpu have a static struct cpu and setting
it up in cstart64.S. But that would mean that we would need extra
handling when using smp functions and that'll look even worse.
Reported-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
---
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 };
We can setup these struct members here and memcpy in smp_setup()
.addr = stap();
.stack = stackptr;
stackptr is accessible in io.c (I would need to add an extern
declaration)
.lowcore = (void *)0;
.active = true;
this temporary struct is then not accessible from smp_setup, so it
can't be memcpy-ed.
if you really want something meaningful in the temporary struct, it has
to be initialized in smp.c and called in io.c (something like
smp_boot_cpu_tmp_setup(&this_cpu_tmp) ), but then still no memcpy.
in the end the struct cpu is needed only to allow interrupts to happen
without crashes, I don't think we strictly need initialization
Ugh, this feels like a quick fix.
But alright, I've just tried setting it up from cstart64.S and it's way
more ugly code so let's stick with this for now.
+
+ /*
+ * 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];
/* Override temporary struct cpu address with permanent one */
will be done
}
}
spin_unlock(&lock);
