Re: [PATCH v2] MIPS: vdso: flush the vdso data page to update it on all processes

Hauke Mehrtens
2016-03-30T21:40:00Z

On 03/30/2016 05:21 PM, Zubair Lutfullah Kakakhel wrote:
> Hi Hauke,
>
> Could you share details of what version of glibc/rfs setup you are using?

Hi,

I am using the musl libc version 1.1.4 in OpenWrt. musl uses the same
vdso code on arm and x86, it just needed some extensions to support the
-ENOSYS return value which is not returned by the other architectures.

I removed the following patches from OpenWrt to activate vdso
gettimeofday in kernel 4.4 again:
target/linux/generic/patches-4.4/206-mips-disable-vdso.patch
target/linux/generic/patches-4.4/340-MIPS-deactivate-gettimeofday-vdso.patch

>
> Thanks.
>
> Regards,
> ZubairLK
>
> On 29/03/16 22:36, Hauke Mehrtens wrote:
>> On 02/21/2016 06:08 PM, Hauke Mehrtens wrote:
>>> Without flushing the vdso data page the vdso call is working on dated
>>> or unsynced data. This resulted in problems where the clock_gettime
>>> vdso call returned a time 6 seconds later after a 3 seconds sleep,
>>> while the syscall reported a time 3 sounds later, like expected. This
>>> happened very often and I got these ping results for example:
>>>
>>> root@OpenWrt:/# ping 192.168.1.255
>>> PING 192.168.1.255 (192.168.1.255): 56 data bytes
>>> 64 bytes from 192.168.1.3: seq=0 ttl=64 time=0.688 ms
>>> 64 bytes from 192.168.1.3: seq=1 ttl=64 time=4294172.045 ms
>>> 64 bytes from 192.168.1.3: seq=2 ttl=64 time=4293968.105 ms
>>> 64 bytes from 192.168.1.3: seq=3 ttl=64 time=4294055.920 ms
>>> 64 bytes from 192.168.1.3: seq=4 ttl=64 time=4294671.913 ms
>>>
>>> This was tested on a Lantiq/Intel VRX288 (MIPS BE 34Kc V5.6 CPU with
>>> two VPEs)
>>>
>>> Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
>>> Cc: <stable@vger.kernel.org> # v4.4+
>>
>> This patch flushes the complete dcache of the CPU if cpu_has_dc_aliases
>> is set.
>>
>> Calling flush_dcache_page(virt_to_page(&vdso_data)); improved the
>> situation a litte bit but did not fix my problem.
>>
>> Could someone from Imagination please look into this problem. The page
>> is linked into many virtual address spaces and when it gets modified by
>> the kernel the user space processes are still accessing partly old data,
>> even when lush_dcache_page() was called.
>>
>>> ---
>>> arch/mips/kernel/vdso.c | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
>>> index 975e997..8b0d974 100644
>>> --- a/arch/mips/kernel/vdso.c
>>> +++ b/arch/mips/kernel/vdso.c
>>> @@ -20,6 +20,8 @@
>>> #include <linux/timekeeper_internal.h>
>>>
>>> #include <asm/abi.h>
>>> +#include <asm/cacheflush.h>
>>> +#include <asm/page.h>
>>> #include <asm/vdso.h>
>>>
>>> /* Kernel-provided data used by the VDSO. */
>>> @@ -85,6 +87,8 @@ void update_vsyscall(struct timekeeper *tk)
>>> }
>>>
>>> vdso_data_write_end(&vdso_data);
>>> + flush_cache_vmap((unsigned long)&vdso_data,
>>> + (unsigned long)&vdso_data + sizeof(vdso_data));
>>> }
>>>
>>> void update_vsyscall_tz(void)
>>> @@ -93,6 +97,8 @@ void update_vsyscall_tz(void)
>>> vdso_data.tz_minuteswest = sys_tz.tz_minuteswest;
>>> vdso_data.tz_dsttime = sys_tz.tz_dsttime;
>>> }
>>> + flush_cache_vmap((unsigned long)&vdso_data,
>>> + (unsigned long)&vdso_data + sizeof(vdso_data));
>>> }
>>>
>>> int arch_setup_additional_pages(struct linux_binprm *bprm, int
>>> uses_interp)
>>>
>>
>>