![]() | |||||||||||||
Messages in this thread |
On Mon, Oct 24, 2005 at 10:45:04PM -0400, Nicolas Pitre wrote: > On Sat, 22 Oct 2005, Russell King wrote: > > Please contact Nicolas Pitre about that - that was my suggestion, > > but ISTR apparantly the overhead is too high. > > Going through a kernel buffer will simply double the overhead. Let's > suppose it should not be a big enough issue to stop the patch from being > merged though (and it looks cleaner that way). However I'd like for the > WARN_ON((unsigned long)frame & 7) to remain as both the kernel and user > buffers should be 64-bit aligned. The WARN_ON is pointless because we guarantee that the stack is always 64-bit aligned on signal handler setup and return. > I don't see how standard COW could not happen. The only difference with > a true write fault as if we used put_user() is that we bypassed the data > abort vector and the code to get the FAR value. Or am I missing > something? pte_write() just says that the page _may_ be writable. It doesn't say that the MMU is programmed to allow writes. If pte_dirty() doesn't return true, that means that the page is _not_ writable from userspace. If you write to it from kernel mode (without using put_user) you'll bypass the MMU read-only protection and may end up writing to a page owned by two separate processes. -- 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/ | ||||||||||||
| Last update: 2005-10-25 07:58 [from the cache] ©2003-2008 | |||||||||||||