On Wed, Jan 21, 2015 at 04:05:33PM +0000, Jon Masters wrote: > On 01/21/2015 10:42 AM, Catalin Marinas wrote: > > On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote: > >> On 01/21/2015 10:23 AM, Catalin Marinas wrote: > >>> I have some questions for the ACPI and EFI folk: > >>> > >>> 1. When booting with ACPI, are the EFI run-time services required for > >>> anything? If yes, Xen may have a bigger problem > >> > >> Yes. At least for some things. For example, installing an Operating > >> System would require that you make runtime services calls to set the > >> BootOrder/BootNext variables, and so on. Further, we use the GetTime > >> service and EFI based reboot to avoid having special drivers. I had > >> those added to SBBR as requirements for that reason. > > > > So what would a kexec'ed kernel do here? Or we usually expect it to be > > short lived and doesn't need reboot, nor GetTime. > > In the use case that I have, it'll use EFI Runtime Servies to handle > both the time of day (which it will need) and to subsequently reboot. > This is currently being worked on (integration into kdump). So the EFI run-time services (and EFI tables) will be preserved across kexec? Could Xen not to something similar? > >>> 2. Could a boot loader (either kernel doing kexec or Xen) emulate the > >>> EFI system/config tables and still make them useful to the kernel but > >>> without EFI_BOOT or EFI_RUNTIME_SERVICES? > >> > >> Yes. But again, without the other required pieces (including the > >> services function pointers in the systab which are required) you'd crash > >> soon after boot trying to make those calls. > > > > My point was whether you can still pass information like RSDP address > > via EFI tables but explicitly disable runtime services so that the > > kernel won't try to make such calls (and crash). > > Yes. As Graeme says, it works just to pass in the ACPI information and > turn off EFI *BUT* it does not work to say you have EFI and then not > provide the correct EFI services. To do so is out of spec, and in fact > it's one reason we weren't able to turn the GetTime service on generally > for x86 - some older x86 boxes didn't implement it originally (another > reason on our end we're requiring all of these services on day one so > that there won't be time for someone to miss them in firmware). OK, thanks for confirming this. So the answer to my second question is "not really". -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
