Hi, > Does the kernel ever switch to use the physical address? No. > Let me give an example (to make sure i understand things correctly) > > 1 - A process in the user space is running (in virtual memory) > > 2- Process requests something from kernel and issues an > interrupt (lets say that process wants to read from a file). > > 3- The 'int' assembly instruction switches from the user space > to kernel space (switch from ring 5 to ring 0, and stack pointer > changes to point kernel stack) > > 4- The process is now running in the kernel space and still with > the SAME VIRTUAL MEMORY(?) as the caller process. > (not sure if this is correct) That is correct. The virtual address space is the same. BUT now the kernel is restricted to (directly) use only the virtual memory beyond 3GB (PAGE_OFFSET). > 5- Now the kernel has to issue an I/O operation to make the hdd > copy the information to memory. > > I have a question at this point. If everything i said is correct > and all. How does the kernel get the information from hdd controller > and move it to user space? > Does it switch to physcal memory? Does it find a page which is empty, > pass address of that page to hdd controller, and mark that page in > the VM table of current process? The kernel does not use physical addresses at point. The closest it gets to that is using bus addresses for DMA. The kernel simply allocates a buffer and inserts a request into the request queue of the device. The block device driver then gets the data from device (may use DMA) and thus buffer is returned. Thanks, Rajat PS: Please use plain text instead of HTML mail. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
