comments about "consistent memory" from here: http://kerneltrap.org/node/7194 might be useful for you too..... On Mon, Oct 10, 2011 at 1:13 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: > while reading this: > > http://linux.die.net/man/2/mlock > > notice that u have to allocate + write to the memory first, before > mlocking it - did u do that? > > (this is to prevent copy-on-write page fault, which means the memory > is allocated.....but is not really resident until written to it....so > allocated memory does not mean the physical memory exist.) > > also, check this function out: drivers/dma/iovlock.c (this function > prepare the memory for IO scatter-gather operation, ie, physical > address must be used, and no segfault is allowed): > > struct dma_pinned_list *dma_pin_iovec_pages(struct iovec *iov, size_t len) > { > > if (!access_ok(VERIFY_WRITE, iov[i].iov_base, iov[i].iov_len)) > goto unpin; > > page_list->nr_pages = num_pages_spanned(&iov[i]); > page_list->base_address = iov[i].iov_base; > > page_list->pages = pages; > pages += page_list->nr_pages; > > /* pin pages down */ > down_read(¤t->mm->mmap_sem); > ret = get_user_pages( > current, > current->mm, > (unsigned long) iov[i].iov_base, > page_list->nr_pages, > 1, /* write */ > 0, /* force */ > page_list->pages, > NULL); > up_read(¤t->mm->mmap_sem); > ========================= > which thus showed the same pattern here, write to it to ensure the TLB > (translation lookaside) exists for the physical address, so there is > no pagefault occurring why hardware read/write the memory bus, which > always goes by physical address (vs everything internal to CPU is > logical/virtual address). > > On Tue, Sep 13, 2011 at 1:45 AM, Florian Bauer > <florian.bauer@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: >> Hi, >> I'm currently writing my first kernel module, but i got stuck with address >> translations. I want my pcie device to access a buffer which was allocated >> in userspace (page aligned, currently smaller than one page to ignore >> scattering). I tried to translate the userspace address to a bus address >> in my ioctrl handler like this: >> >> void __user *data = arg; >> down_read(¤t->mm->mmap_sem); >> get_user_pages(current, current->mm, (unsigned long)data, len/*1*/, 1, 0, >> &pages, NULL); >> up_read(¤t->mm->mmap_sem); >> void* kvaddr = kmap(pages[0]); >> unsigned long baddr = virt_to_bus(kaddr); >> kunmap(pages[0]); >> page_cache_release(pages[0]); >> //... >> >> data is page-aligned and was locked in userspace with mlock. >> There is some address in baddr, but the device does not write to the >> correct location and sometimes causes kernel freezes. Can someone tell me, >> what is wrong with this code?TheI device works with a address, that was >> received in different way (closed source driver). >> I use 32 bit Ubuntu with an 2.6.32 kernel. >> >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > > > > -- > Regards, > Peter Teoh > -- Regards, Peter Teoh _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
