Messages in this thread | | | Date | Fri, 2 Jul 2010 01:59:11 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [patch 071/149] ARM: 6166/1: Proper prefetch abort handling on pre-ARMv6 |
| |
On Thu, Jul 01, 2010 at 11:48:37PM +0100, Russell King wrote: > On Fri, Jul 02, 2010 at 01:25:41AM +0300, Kirill A. Shutemov wrote: > > On Thu, Jul 01, 2010 at 03:17:28PM -0700, Greg KH wrote: > > > We (well, I) like to keep the commit log identical to what is upstream > > > just to make things easier all around. Otherwise people start asking > > > for spelling fixes, clarifications, and all sorts of other stuff (like > > > this.) > > > > Ok, fair enough. > > > > I asked for it because I was confused by this commit message while > > investigate (the same) problem on ARMv7 CPU. > > You shouldn't get anywhere near this on ARMv7, because we know the cause > of the prefetch abort on those CPUs. > > On pre-ARMv6 CPUs, we always treat all prefetch aborts as a translation > faults. The problem which this commit addresses occurs when userspace > tries to execute code above TASK_SIZE - we're sent into a loop of prefetch > aborts (because we are unable to determine that it is a permission fault.) > > ARMv6 and ARMv7 CPUs have an instruction fault status register, which > tells us why the abort happened. On these CPUs, permission faults go > nowhere near the translation fault handler.
I know it. I was involved in writing this code.
> One possibility is that for some reason you're using the legacy prefetch > abort code or pre-IFSR code, which will always tell the kernel that its > a translation fault - and in this case, this patch would improve the > situation. What kernel version are you using?
2.6.32
> The commit message is accurate for the kernel version to which it was > originally applied.
Simple testcase:
#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h>
int main(int argc, char **argv) { int fd; void (*p)(void);
fd = open("/dev/urandom", O_RDONLY); read(0, &p, sizeof(p)); printf("p: %p\n", p); p(); return 0; }
If you run this test in loop on kernel without the patch you'll finally get hung instead SIGSEGV.
It seems the patch fixes more than it was written for. :)
-- Kirill A. Shutemov
| |