| Message ID | 20210323215819.4161164-2-hca@linux.ibm.com |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | s390 vdso fixes | expand |
On Tue, Mar 23, 2021 at 10:58:17PM +0100, Heiko Carstens wrote: > 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. > > When converting the assembler code to C it was forgotten to tell user > space in which direction the clock has to be adjusted. > > 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 providing the missing value to user space. > > Fixes: 4bff8cb54502 ("s390: convert to GENERIC_VDSO") > Cc: <stable@vger.kernel.org> # 5.10 > Signed-off-by: Heiko Carstens <hca@linux.ibm.com> > --- > arch/s390/kernel/time.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c > index 165da961f901..e37285a5101b 100644 > --- a/arch/s390/kernel/time.c > +++ b/arch/s390/kernel/time.c > @@ -382,6 +382,7 @@ static void clock_sync_global(unsigned long delta) > tod_steering_delta); > tod_steering_end = now + (abs(tod_steering_delta) << 15); > vdso_data->arch_data.tod_steering_end = tod_steering_end; > + vdso_data->arch_data.tod_steering_delta = tod_steering_delta; ..and yet another bug: __arch_get_hw_counter() tests if tod_steering_delta is negative. It makes sense to give tod_steering_delta the correct type: diff --git a/arch/s390/include/asm/vdso/data.h b/arch/s390/include/asm/vdso/data.h index 7b3cdb4a5f48..73ee89142666 100644 --- 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; };
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index 165da961f901..e37285a5101b 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -382,6 +382,7 @@ static void clock_sync_global(unsigned long delta) tod_steering_delta); tod_steering_end = now + (abs(tod_steering_delta) << 15); vdso_data->arch_data.tod_steering_end = tod_steering_end; + vdso_data->arch_data.tod_steering_delta = tod_steering_delta; /* Update LPAR offset. */ if (ptff_query(PTFF_QTO) && ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
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. When converting the assembler code to C it was forgotten to tell user space in which direction the clock has to be adjusted. 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 providing the missing value to user space. Fixes: 4bff8cb54502 ("s390: convert to GENERIC_VDSO") Cc: <stable@vger.kernel.org> # 5.10 Signed-off-by: Heiko Carstens <hca@linux.ibm.com> --- arch/s390/kernel/time.c | 1 + 1 file changed, 1 insertion(+)