kmalloc 分配实际上不是连续的吗？
Is kmalloc allocation not virtually contiguous?
我发现 kmalloc returns 物理上和虚拟上连续的内存。
我写了一些代码来观察行为，但似乎只有物理内存是连续的而不是虚拟内存。我有没有搞错？
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/moduleparam.h>
MODULE_LICENSE("GPL");
static char *ptr;
int alloc_size = 1024;
module_param(alloc_size, int, 0);
static int test_hello_init(void)
{
ptr = kmalloc(alloc_size,GFP_ATOMIC);
if(!ptr) {
/* handle error */
pr_err("memory allocation failed\n");
return -ENOMEM;
} else {
pr_info("Memory allocated successfully:%p\t%p\n", ptr, ptr+100);
pr_info("Physical address:%llx\t %llx\n", virt_to_phys(ptr), virt_to_phys(ptr+100));
}
return 0;
}
static void test_hello_exit(void)
{
kfree(ptr);
pr_info("Memory freed\n");
}
module_init(test_hello_init);
module_exit(test_hello_exit);
dmesg 输出：
Memory allocated successfully:0000000083318b28 000000001fba1614
Physical address:1d5d09c00 1d5d09c64
打印内核指针通常不是一个好主意，因为它基本上意味着将内核地址泄露给用户space，所以当在printk()中使用%p（或类似的宏[= =14=] 等），内核试图保护自己，不打印真实地址。相反，它会为该地址打印一个不同的散列唯一标识符。
如果你真的想要打印那个地址，你可以使用%px.
来自 How to get printk format specifiers right (web) or Documentation/core-api/printk-formats.rst (git):
Pointer Types
Pointers printed without a specifier extension (i.e unadorned %p) are
hashed to give a unique identifier without leaking kernel addresses to user
space. On 64 bit machines the first 32 bits are zeroed. If you really
want the address see %px below.
%p abcdef12 or 00000000abcdef12
然后，下面是：
Unmodified Addresses
%px 01234567 or 0123456789abcdef
For printing pointers when you really want to print the address. Please
consider whether or not you are leaking sensitive information about the
Kernel layout in memory before printing pointers with %px. %px is
functionally equivalent to %lx. %px is preferred to %lx because it is more
uniquely grep'able. If, in the future, we need to modify the way the Kernel
handles printing pointers it will be nice to be able to find the call
sites.
我发现 kmalloc returns 物理上和虚拟上连续的内存。
我写了一些代码来观察行为，但似乎只有物理内存是连续的而不是虚拟内存。我有没有搞错？
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/moduleparam.h>
MODULE_LICENSE("GPL");
static char *ptr;
int alloc_size = 1024;
module_param(alloc_size, int, 0);
static int test_hello_init(void)
{
ptr = kmalloc(alloc_size,GFP_ATOMIC);
if(!ptr) {
/* handle error */
pr_err("memory allocation failed\n");
return -ENOMEM;
} else {
pr_info("Memory allocated successfully:%p\t%p\n", ptr, ptr+100);
pr_info("Physical address:%llx\t %llx\n", virt_to_phys(ptr), virt_to_phys(ptr+100));
}
return 0;
}
static void test_hello_exit(void)
{
kfree(ptr);
pr_info("Memory freed\n");
}
module_init(test_hello_init);
module_exit(test_hello_exit);
dmesg 输出：
Memory allocated successfully:0000000083318b28 000000001fba1614
Physical address:1d5d09c00 1d5d09c64
打印内核指针通常不是一个好主意，因为它基本上意味着将内核地址泄露给用户space，所以当在printk()中使用%p（或类似的宏[= =14=] 等），内核试图保护自己，不打印真实地址。相反，它会为该地址打印一个不同的散列唯一标识符。
如果你真的想要打印那个地址，你可以使用%px.
来自 How to get printk format specifiers right (web) or Documentation/core-api/printk-formats.rst (git):
Pointer Types
Pointers printed without a specifier extension (i.e unadorned
%p) are hashed to give a unique identifier without leaking kernel addresses to user space. On 64 bit machines the first 32 bits are zeroed. If you really want the address see%pxbelow.%p abcdef12 or 00000000abcdef12
然后，下面是：
Unmodified Addresses
%px 01234567 or 0123456789abcdefFor printing pointers when you really want to print the address. Please consider whether or not you are leaking sensitive information about the Kernel layout in memory before printing pointers with
%px.%pxis functionally equivalent to%lx.%pxis preferred to%lxbecause it is more uniquely grep'able. If, in the future, we need to modify the way the Kernel handles printing pointers it will be nice to be able to find the call sites.