Messages in this thread | | | Date | Thu, 2 Nov 2006 19:33:48 +0000 | From | "Miguel Ojeda" <> | Subject | Re: [PATCH update6] drivers: add LCD support |
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On 11/2/06, Andrew Morton <akpm@osdl.org> wrote: > On Thu, 2 Nov 2006 14:44:56 +0000 > "Miguel Ojeda" <maxextreme@gmail.com> wrote: > > > > Now let's say that some of the kernel frame buffer data are in the > > > data cache and never be invalidate during this example. The > > > > Sorry, I don't understand what do you mean with this sentence. > > Some CPU architectures experience what Documentation/cachetlb.txt calls > "virtual aliasing in the data cache". > > If you map the same physical page at virtual address A1 and also at another > virtual address A2 then writes to address A1 do not necessarily appear > correctly at address A2. This because the write to A1 is stuck in the CPU > cache and the CPU hardware doesn't know that read from A2 is accessing the > same page. > > The solutions to this are: > > a) add lots of flushing everywhere (see Documentation/cachetlb.txt, I > guess) (this documentation is maddening: it uses the term "flush" for > both writeback and for invalidation. In this context, > flush==writeback). > > b) If you select the correct virtual addresses for A1 and A2 (ie: ensure > that the mmap() handler returns an address which correlates with the > page's kernel address) then apparently the aliasing goes away. > > So, for example, if the kernel's view of the page is at 0xd0102000 > then you make sure that userspace's address for the page is at > 0xnnn02000 (for some length of nnn). > > I don't know what the mmap handler has to do to arrange for this to > happen. > > c) add `depends on x86' to your Kconfig ;)
I really like portable stuff :)
> > > davem and rmk are (amongst others) the guys for this stuff. afaik it isn't > documented anywhere. >
Whoa, thanks you for the long explanation. May 2.6.18-new vmalloc related functions help correlating userspace & kernel addresses? I will try them and come with an answer tomorrow.
Quoting http://lwn.net/Articles/2.6-kernel-api/
"Some functions have been added to make it easy for kernel code to allocate a buffer with vmalloc() and map it into user space. They are:
void *vmalloc_user(unsigned long size); void *vmalloc_32_user(unsigned long size); int remap_vmalloc_range(struct vm_area_struct *vma, void *addr, unsigned long pgoff);
The first two functions are a form of vmalloc() which obtain memory intended to be mapped into user space; among other things, they zero the entire range to avoid leaking data. vmalloc_32_user() allocates low memory only. A call to remap_vmalloc_range() will complete the job; it will refuse, however, to remap memory which has not been allocated with one of the two functions above." - 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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