s390/vdso: fix tod_steering_delta type

BugLink: https://bugs.launchpad.net/bugs/1923069
commit b24bacd67ffddd9192c4745500fd6f73dbfe565e upstream.

The s390 specific vdso function __arch_get_hw_counter() is supposed to
consider tod clock steering.

If a tod clock steering event happens and the tod clock is set to a
new value __arch_get_hw_counter() will not return the real tod clock
value but slowly drift it from the old delta until the returned value
finally matches the real tod clock value again.

Unfortunately the type of tod_steering_delta unsigned while it is
supposed to be signed. It depends on if tod_steering_delta is negative
or positive in which direction the vdso code drifts the clock value.

Worst case is now that instead of drifting the clock slowly it will
jump into the opposite direction by a factor of two.

Fix this by simply making tod_steering_delta signed.

Fixes: 4bff8cb54502 ("s390: convert to GENERIC_VDSO")
Cc: <stable@vger.kernel.org> # 5.10
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

diff --git a/arch/s390/include/asm/vdso/data.h b/arch/s390/include/asm/vdso/data.h
index 7b3cdb4a5f48148085608ec00cb48131feaaf416..73ee8914266629559ad11053f79984ac49b4b97e 100644 (file)
--- a/arch/s390/include/asm/vdso/data.h
+++ b/arch/s390/include/asm/vdso/data.h
@@ -6,7 +6,7 @@
 #include <vdso/datapage.h>
 
 struct arch_vdso_data {
-       __u64 tod_steering_delta;
+       __s64 tod_steering_delta;
        __u64 tod_steering_end;
 };