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

[Hauke Mehrtens <hauke@hauke-m.de>]

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)
>