From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Wurmsdobler Subject: mmap of 8GB reserved memory using remap_pfn_range Date: Wed, 05 May 2010 14:15:48 +0100 Message-ID: <4BE16F84.30205@wurmsdobler.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-newbie-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: linux-newbie@vger.kernel.org Hello, I am using 64bit Ubuntu 9.04, kernel 2.8.28, on a PC equipped with 12GB RAM. I would like to capture and store data into a reserved memory area, 8GB big and above 4GB. This memory area is currently being reserved at boot time by passing "mem=4G memmap=8G$4G" to the kernel. (Interestingly enough, "free" reports only 3GB memory, a mismatch I do not quite understand yet.) I wrote a small char device driver that does an ioremap of the entire reserved physical memory area and implements the mmap file operation using remap_pfn_range. A user space application succeeds in opening the dev file corresponding to the char driver and in calling mmap. Unfortunatley, when it tries to read/write to/from the mmaped area, the kernel is complaining with a "Corrupted page table at address ..." and a register dump. This is in essence what my code does. In my char driver I #define 8GB reserved memory at an offset of 4GB: #define RAW_DATA_SIZE 0x200000000UL #define RAW_DATA_OFFSET 0x100000000UL In init_modulule, I ioremap the physical memory to kernel virtual memory, and in addition set it to zero: rawdataStart = ioremap(RAW_DATA_OFFSET, RAW_DATA_SIZE); memset(rawdataStart, 0, RAW_DATA_SIZE); After some parameter checking, the mmap file operation function does: remap_pfn_range(vma, vma->vm_start, (unsigned long) rawdataStart, RAW_DATA_SIZE, PAGE_SHARED); In user space, the mmap call on the corresponding file descriptor still works: fd = open("/dev/rawdata", O_RDWR | O_SYNC); mptr = mmap(0, RAW_DATA_SIZE, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 4096); but the assignment "mptr[0] = 'a'" fails with the dmesg output below. What am I doing wrong? Do I need to loop through smaller chunks when calling remap_pfn_range? Help is very much appreciated. Kind regards, peter [ 481.669633] rmem_test: opened [ 481.669696] rmem_test: mmap [ 481.717016] rmem_test: mmap OK [ 481.717157] rmem_map: Corrupted page table at address 7f63179e1000 [ 481.717222] PGD b6471067 PUD b44eb067 PMD b55ed067 PTE 7c20011890000227 [ 481.717434] Bad pagetable: 000d [#3] SMP [ 481.717567] last sysfs file: /sys/devices/system/cpu/cpu7/cpufreq/scaling_governor [ 481.717649] CPU 0 [ 481.717741] Modules linked in: rmem_test nfs lockd nfs_acl sunrpc input_polldev video output lp parport snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd soundcore snd_page_alloc pcspkr psmouse serio_raw iTCO_wdt iTCO_vendor_support usbhid nvidia(P) ohci1394 r8169 mii ieee1394 floppy [ 481.719030] Pid: 3781, comm: rmem_map Tainted: P D 2.6.28.paw2 #1 [ 481.719094] RIP: 0033:[<00000000004006bc>] [<00000000004006bc>] 0x4006bc [ 481.719198] RSP: 002b:00007fff1f442ee0 EFLAGS: 00010206 [ 481.719260] RAX: 00007f63179e1000 RBX: 0000000000400730 RCX: 0000000000000002 [ 481.719325] RDX: 00007f6517d4e9c0 RSI: 00007f6517f6e029 RDI: 00007f6517f6e027 [ 481.719390] RBP: 00007fff1f442f00 R08: 0000000000000001 R09: 0000000000000002 [ 481.719455] R10: 0000000000000022 R11: 00000000ffffffff R12: 0000000000400550 [ 481.719520] R13: 00007fff1f442fd0 R14: 0000000000000000 R15: 0000000000000000 [ 481.719586] FS: 00007f6517f666f0(0000) GS:ffffffff80a8f000(0000) knlGS:0000000000000000 [ 481.719667] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 481.719730] CR2: 00007f63179e1000 CR3: 00000000b44e5000 CR4: 00000000000006a0 [ 481.719795] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 481.719860] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 481.719926] Process rmem_map (pid: 3781, threadinfo ffff8800b446e000, task ffff8800b8cf4320) [ 481.720007] [ 481.720061] RIP [<00000000004006bc>] 0x4006bc [ 481.720158] RSP <00007fff1f442ee0> [ 481.720236] ---[ end trace e47eba847a88b683 ]--- [ 481.756598] rmem_test: released -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" 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.linux-learn.org/faqs