Messages in this thread |  | | | From | Vitaly Mayatskikh <> | | Subject | Re: [PATCH] x86: Optimize tail handling for copy_user | | Date | Tue, 29 Jul 2008 17:24:09 +0200 |
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Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Mon, 28 Jul 2008, Vitaly Mayatskikh wrote: >> >> Reduce protection faults count in copy_user_handle_tail routine by >> limiting clear length to the end of page as was suggested by Linus. > > No, you did it wrong. > > The page _clearing_ has to be to the end of the copy. Yes, in practice, I > don't think the kernel actually very often does "copy_from_user()" calls > that are page crossers in the kernel, but they do happen. > > It's the _copy_ part that needn't cross pages, because we know that > something faulted, and we _know_ that it wasn't the clearing. > > Really: the clearing should be just a "memset()" with no limitations. It > can never fault without it being a serious bug, and then we should not fix > it up, but we should oops!
Right. I will take your code discussed previously. The only question is: what will be a good place for *_IS_USERSPACE and CLEAR_REMAINDER flags definitions and assembly macro ALIGN_DESTINATION (common for copy_user_64.S and copy_user_nocache_64.S)? I have a new file include/asm-x86/copy_user.h at the moment, but not sure if you will think it's ok to put that stuff here:
include/asm-x86/copy_user.h: #ifndef _COPY_USER_H #define _COPY_USER_H
/* Flags for copy_user_handle_tail */ #define CLEAR_REMAINDER 1 #define DEST_IS_USERSPACE 2 #define SOURCE_IS_USERSPACE 4 /* Align destination */ #define FIX_ALIGNMENT 1 #define BYTES_LEFT_IN_PAGE(ptr) \ (unsigned long)((PAGE_MASK & ((long)(ptr) + PAGE_SIZE)) - (long)(ptr))
#ifdef __ASSEMBLY__ .macro ALIGN_DESTINATION ... #endif /* FIX_ALIGNMENT */ .endm #endif /* __ASSEMBLY__ */ #endif /* _COPY_USER_H */ -- wbr, Vitaly
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