Messages in this thread | | | Date | Mon, 31 Oct 2005 22:50:11 +0000 | From | Russell King <> | Subject | Re: [PATCH 2/9] mm: arm ready for split ptlock |
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On Mon, Oct 31, 2005 at 11:34:39PM +0100, Jesper Juhl wrote: > On 10/31/05, Russell King <rmk+lkml@arm.linux.org.uk> wrote: > > On Mon, Oct 31, 2005 at 11:19:21PM +0100, Jesper Juhl wrote: > > > Yes, I removed verify_area() since it was just a wrapper for access_ok(). > > > If verify_area() was/is needed, then access_ok() should be just fine > > > as a replacement as far as I can see. > > > > Except verify_area() would pre-fault the pages in whereas access_ok() > > just verifies that the address is a user page. That's quite important > > in this case because in order to fault the page in, we need to use > > put_user() to get the permission checking correct. > > > > However, we can't use put_user() because then the cmpxchg emulation > > becomes completely non-atomic. > > > Colour me stupid, but I don't see how that can be. > > Looking at verify_area() from 2.6.13 - the arm version ( > http://sosdg.org/~coywolf/lxr/source/include/asm-arm/uaccess.h?v=2.6.13#L81 > ) : > > static inline int __deprecated verify_area(int type, const void __user > *addr, unsigned long size) > { > return access_ok(type, addr, size) ? 0 : -EFAULT; > } > > How will this cause pre-faulting if a call to access_ok() will not? > Please enlighten me.
This is true because we haven't had this requirement up until the introduction of this. I am referring to some functionality which was present a while back in the kernel - the old version of verify_area which, when passed a VERIFY_WRITE argument, would prefault the pages... as required for some i386 CPUs.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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