如何使用内核模块直接访问保留内存？

I'm trying to limit the OS (Ubuntu Server 15.04) to a certain memory usage and reserve the rest but write a kernel module to read/write to the reserved memory. I figured out how to limit the usage/reserve memory using the kernel parameters "mem=4G memmap=4G@0 memmap=4G$4G" (4GB for OS and 4GB reserved, split at 4GB point) but I don't know how DMA to reserved memory works with kernel modules. I was thinking just create a proc file but I'm not sure if you can create one outside of the OS's allocated memory.

我正在尝试将操作系统（Ubuntu Server 15.04）限制为某种内存使用情况，并保留其余内存但写入内核模块以读取/写入保留内存。我想出了如何使用内核参数“mem = 4G memmap = 4G @ 0 memmap = 4G $ 4G”限制使用/预留内存（OS为4GB，保留4GB，分为4GB）但我不知道如何DMA到保留的内存与内核模块一起使用。我在想只是创建一个proc文件，但我不确定你是否可以在操作系统分配的内存之外创建一个。

Any suggestions? Thanks!

有什么建议么？谢谢！

Edit: This is for research so it doesn't need to be "nice"

编辑：这是为了研究，所以它不需要“很好”

Update: Maybe I don't need to write a kernel module. I just found this and I'm going to give it a shot: http://elinux.org/Memory_Management#Reserving_.28and_accessing.29_the_top_of_memory_on_startup

更新：也许我不需要编写内核模块。我刚发现了这个，我打算试一试：http：//elinux.org/Memory_Management#Reserving_.28and_accessing.29_the_top_of_memory_on_startup

Update: I tried the link above but I segfault whenever I try to write. Here's my code:

更新：我尝试了上面的链接，但每当我尝试编写时我都会遇到错误。这是我的代码：

    #include <fcntl.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/mann.h>

    #define RESERVED_MEMORY_SIZE 0x100000000

    int main() {
            int fd;
            char *reserved_memory;

            fd = open("/dev/mem", O_RDWR | O_SYNC);
            reserved_memory = (char *) mmap(0, RESERVED_MEMORY_SIZE, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 4096);
            reserved_memory[0] = 'a';
            return 0;
    }

dmesg shows:

dmesg显示：

    a.out[1167]: segfault at ffffffffffffffff ip 00000000004005d7 sp 00007ffeffccbd80 error 7 in a.out[400000+1000]

For kicks I tried reserved_memory[1]:

对于踢，我尝试了reserved_memory [1]：

    a.out[1180]: segfault at 0 ip 00000000004005db sp 00007ffc388d77b0 error 6 in a.out[400000+1000]

I'll look into the format of those messages so I can figure out what it's telling me.

我将研究这些消息的格式，以便我能够弄清楚它告诉我的内容。

Update:

更新：

I found this question by somebody with the same issue as me however the only solution appears to be a kernel rebuild. I'm going to try to avoid this so maybe my best option is a custom kernel module again. accessing mmaped /dev/mem?

我发现这个问题与我有同样的问题但是唯一的解决方案似乎是内核重建。我将尽力避免这种情况，所以也许我最好的选择是再次定制内核模块。访问mmaped / dev / mem？

1 个解决方案

#1

Ok, so I think I solved it. Turns out I just didn't understand how mmap works and I guess the kernel has no restriction on writing/reading /dev/mem if it's in reserved memory. Below are two programs that will write to my reserved spot in memory and read from it.

好的，所以我想我解决了。原来我只是不明白mmap是如何工作的，我想内核对写/读/ dev / mem没有限制，如果它在保留的内存中。下面是两个程序，它们将写入我在内存中的保留位置并从中读取。

Write "Hello World!":

写下“Hello World！”：

    #include <errno.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <sys/mman.h>

    #define RESERVED_MEMORY_OFFSET  0x100000000     /* Offset is 4GB */

    int main() {
            int fd;
            char *reserved_memory;
            char *buffer = "Hello World!";

            fd = open("/dev/mem", O_RDWR | O_SYNC):
            /* Returns a pointer to the 4GB point in /dev/mem - the start of my reserved memory. Only mapping 4096 bytes. */
            reserved_memory = (char *) mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, RESERVED_MEMORY_OFFSET);
            if (reserved_memory == MAP_FAILED) {
                    printf("Failed to creating mapping.\n");
                    printf("ERRNO: %s\n", strerror(errno));
                    return -1;
            }
            sprintf(reserved_memory, "%s", buffer);
            return 0;
    }

Read from beginning of reserved memory:

从保留存储器的开头读取：

    #include <errno.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <sys/mman.h>

    #define RESERVED_MEMORY_OFFSET  0x100000000     /* Offset is 4GB */

    int main() {
            int fd;
            char *reserved_memory;
            char buffer[13];

            fd = open("/dev/mem", O_RDWR | O_SYNC):
            /* Returns a pointer to the 4GB point in /dev/mem - the start of my reserved memory. Only mapping 4096 bytes. */
            reserved_memory = (char *) mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, RESERVED_MEMORY_OFFSET);
            if (reserved_memory == MAP_FAILED) {
                    printf("Failed to creating mapping.\n");
                    printf("ERRNO: %s\n", strerror(errno));
                    return -1;
            }
            snprintf(buffer, 13, "%s", reserved_memory);
            printf("%s\n", buffer);
            return 0;
    }

Special thanks to @knm241!

特别感谢@ knm241！

#1