On 02/19/13 19:41, Gleb Natapov wrote: > On Tue, Feb 19, 2013 at 06:35:03PM +0000, David Woodhouse wrote: >> On Tue, 2013-02-19 at 20:13 +0200, Gleb Natapov wrote: >>> >>>> I take it you mean copy 0xfffe0000 to 0xe0000? That would not be >>> fun. >>>> SeaBIOS would need to detect that it's in the state (it's definitely >>>> not correct to do that on real-hardware or on "working" kvm >>>> instances), then setup a trampoline somewhere outside of >>>> 0xe0000-0xfffff to do the memcpy, jump to that trampoline, copy the >>>> memory, restore segment registers, and then jump to 0xfffffff0. >>>> That's a lot of kvm specific code to add to seabios as a workaround >>>> and it seems fragile anyway. >>>> >>> Isn't this exactly what qemu_prep_reset() is doing now? >> >> No. It doesn't do the trampoline thing because it doesn't *have* to; >> it's copying an identical copy of the code back over itself. >> > Ah, yes of course. So does CSM takes the whole 0xe0000-0xfffff segment or > it leaves OVMF code there somewhere. CSM reset code can jump into OVMF > code in 0xe0000-0xfffff range and let it do the copy.
I think the only thing you could know about the UEFI environment (call-wise or jump-wise) while in the CSM is ReverseThunkCallSegment / ReverseThunkCallOffset. Theoretically those allow the CSM to call back into EfiCompatibility (32-bit protected mode environment). Some problems: - Using the reverse thunk might only be allowed if we ended up in real mode coming through the forward thunk to begin with. When qemu/kvm simply jumps to 0xffff0 (reset request from guest OS), this doesn't hold. - Currently no reverse thunk functions are defined in the CSM spec, and the implementation in TianoCore seems ... absent. The directory "IntelFrameworkModulePkg/Csm/LegacyBiosDxe/Ipf" appears to contain some incomplete Itanium assembly. Anyway David is fixing qemu to reset the PAMs at hard reset, so OVMF should show up again in the f-segment, accomodating older kvm hosts. Laszlo ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_feb _______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
