> -----Original Message----- > From: StephanT [mailto:stman937-linewbie@xxxxxxxxx] > Sent: Tuesday, October 18, 2011 6:01 PM > To: Jeff Haran; kernelnewbies > Subject: Re: How can I test if a physical address is already mapped or not. > > > > >> Yes you are right when you are in user space. However in a kernel > >> module this would be physical address. > > > > Nope. Unless you are using some really strange processor that I am not > familiar > > with, a memory read is a memory read. *pReg is going to read what's at > > virtual address 0xc0000000 regardless of whether you are executing in user > or > > kernel context. I know it's going to work this way on a PC with an Intel x86 > > processor. > > > > > OK, but how do you explain I can read 0xC0000000 and I get kicked out if > I try 0x00100000. I can only assume that there is nothing mapped to virtual address 0x00100000. On a 32 bit PC, the bottom 3 GB of virtual memory is by default mapped to user space, so if anything you are accessing memory in the current process' virtual memory. > > >> The 0xC0000000 falls under PCI address range. I guess on a PC Linux > >> just doesn't map this address range or it maps it one2one (phys==virt) > >> I can dereference this address and I get something plausible. > > > > On most 32 bit Intel processors running "standard" Linux 0xC0000000 is > > the first address of kernel VM. This is a function of kernel configuration, but > > it's this way by default. It's still a virtual address. So yes, on your > > PC virtual address 0xC0000000 is mapped to physical RAM. > > > > > Would this mean by reading the 0xC0000000 I am reading the Linux code not > PCI registers? First part of the page table, I think. I don't really remember what the kernel maps down there but I don't think its code. Read the Gorman book. It's a lot to get through, but you'll likely learn a lot. There might even be something newer out there. Jeff Haran _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
