Hi Sabela, On Fri, Sep 11, 2015 at 8:29 PM, Sabela Ramos Garea <sabelaraga@gmail.com> wrote:
Sorry, little mistake copypasting and cleaning. The pages and vma structs should look like that:
struct page *pages --> struct page *pages[MAX_PAGES]; struct vma_area_struct *vma --> struct vma_area_struct *vma[MAX_PAGES];
Where MAX_PAGES is defined to 5.
Sabela.
2015-09-11 16:07 GMT+02:00 Sabela Ramos Garea <sabelaraga@gmail.com>:
Dear all,
For research purposes I need some userspace memory pages to be in uncacheable mode. I am using two different Intel architectures (Sandy Bridge and Haswell) and two different kernels (2.6.32-358 and 3.19.0-28).
The non-temporal stores from Intel assembly are not a valid solution so I am programming a kernel module that gets a set of pages from user space reserved with posix_memalign (get_user_pages) and then sets them as uncacheable (I have tried set_pages_uc and set_pages_array_uc). When I use one page, the access times are not very coherent and with more than one page the module crashes (in both architectures and both kernels).
I wonder if I am using the correct approach or if I have to use kernel space pages in order to work with uncacheable memory. Or if I have to remap the memory. Just in case it makes it clearer, I am attaching the relevant lines of a kernel module function that should set the pages as uncacheable. (This function is the .write of a misc device; count is treated as the number of pages).
Best and Thanks,
Sabela.
struct page *pages; //defined outside in order to be able to set them to WB in the release function. int numpages;
static ssize_t setup_memory(struct file *filp, const char __user *buf, size_t count, loff_t * ppos) { int res; struct vm_area_struct *vmas;
shouldn't this be rounded this up?
numpages = count/4096;
down_read(¤t->mm->mmap_sem); res = get_user_pages(current, current->mm, (unsigned long) buf, numpages, /* Number of pages */ 0, /* Do want to write into it */ 1, /* do force */ &pages, &vmas); up_read(¤t->mm->mmap_sem);
numpages=res;
if (res > 0) { set_pages_uc(pages, numpages); /* Uncached */
what about high-mem pages. set_memory_uc does __pa, so perhaps that's the reason for your kernel oops?
printk("Write: %d pages set as uncacheable\n",numpages); } else{ pr_err("Couldn't get pages to set them as UC :(\n"); return -EAGAIN; } }
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