2010/10/9 Dev Null <devnullfin@xxxxxxxxx>: > Hello Folks, > I would like to know the core differences between Kernel logical > address(KLA) and kernel virtual address(KVA). > I know few differences about them like: > 1. KLA is somewhat similar to Physical address but it has some logical base > address and offset such that it is not pointing to physical address. > 2. KLA --> kmalloc , KVA --> vmalloc > 3. Sometimes, all KLA are KVA, but many KVA are not KLA. > In Linux, how can you point to actual physical address? Does that mean there > is one more layer of MMU between KLA and physical address? > Please feel free to comment on my questions and help me to get the clear > understanding of MMU of Linux. http://www.linuxdriver.co.il/ldd3/chp-15-sect-1.shtml Kernel logical addresses These make up the normal address space of the kernel. These addresses map some portion (perhaps all) of main memory and are often treated as if they were physical addresses. On most architectures, logical addresses and their associated physical addresses differ only by a constant offset. Logical addresses use the hardware's native pointer size and, therefore, may be unable to address all of physical memory on heavily equipped 32-bit systems. Logical addresses are usually stored in variables of type unsigned long or void *. Memory returned from kmalloc has a kernel logical address. Kernel virtual addresses Kernel virtual addresses are similar to logical addresses in that they are a mapping from a kernel-space address to a physical address. Kernel virtual addresses do not necessarily have the linear, one-to-one mapping to physical addresses that characterize the logical address space, however. All logical addresses are kernel virtual addresses, but many kernel virtual addresses are not logical addresses. For example, memory allocated by vmalloc has a virtual address (but no direct physical mapping). The kmap function (described later in this chapter) also returns virtual addresses. Virtual addresses are usually stored in pointer variables. > Thanks, > Dev Null -- Best Regards Lin -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
