On 08/06/13 00:52, James Bottomley wrote: > On Mon, 2013-08-05 at 23:55 +0200, Laszlo Ersek wrote: >> On 08/05/13 23:41, Borislav Petkov wrote: >>> On Mon, Aug 05, 2013 at 02:37:08PM -0700, H. Peter Anvin wrote: >>>> All of this would be a non-problem if there weren't buggy >>>> implementations which can't run *without* SetVirtualAddressMap(). >>> >>> Oh, you mean, if we were to call the runtime services through their >>> physical addresses? >> >> I heard that there was a (U)EFI firmware implementation that didn't even >> implement SetVirtualAddressMap(). It was okay because the main OS for >> that platform didn't want to call it, it thunked to physical mode for >> each runtime service call. >> >> (This is not hearsay; I'm omitting the specifics because I'm not sure if >> I'm allowed to give any. I've heard about this stuff from a direct >> colleague who used to work on these systems.) > > That's actually the way all non-x86 unix systems operate. If you look > in the firmware mechanisms for almost every non-x86 system in the Linux > kernel architecture directories they do this if they have to access > firmware from Linux (we do it a lot on parisc to get the IODC to give us > the device inventory for instance). > > I strongly suspect the origin of this weirdness is that once upon a time > windows didn't run with a separated address space and so needed a way of > accessing firmware in the same address space, hence the pointer > relocation trick, but even windows hasn't needed this for a while.
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