On 16.03.21 15:06, Ard Biesheuvel wrote: > On Tue, 16 Mar 2021 at 14:25, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: >> >> On 16.03.21 10:33, Ilias Apalodimas wrote: >>> Hi Shawn, >>> >>>>>>>>> So an installer either needs to set the EFI variable, or pass >>>>>>>>> efi=novamap on the first boot. Note that there are no arm64 EFI >>>>>>>>> systems known where efi=novamap causes problems. In fact, I would >>>>>>>>> prefer to stop using SetVirtualAddressMap() altogether, as it does not >>>>>>>>> provide any benefit whatsoever. So perhaps we should make efi=novamap >>>>>>>>> the default and be done with it. >>>>>>>>> >>>>>>>>> Broken poweroff is hardly a showstopper for an installer, given that >>>>>>>>> we cannot even install GRUB correctly. >>>>>>>>> >>>>>>>>> In summary, I am more than happy to collaborate constructively on this >>>>>>>>> (which is why I wrote the patch), but I don't think we're at a point >>>>>>>>> yet where this is the only thing standing in our way when it comes to >>>>>>>>> a smooth out-of-the-box Linux installation experience. >>>>>>>> >>>>>>>> There might be more to be done for getting a smooth Linux installation >>>>>>>> experience. But IMHO, this `OverrideSupported` thing is definitely >>>>>>>> a big step to that. >>>>>>>> >>>>>>> >>>>>>> So the problem here seems to be that grub-install (or efibootmgr) >>>>>>> tolerates efivarfs being absent entirely, but bails out if it exists >>>>>>> but gives an error when trying to access it, right? >>>>>> >>>>>> Yes, with EFI variables runtime service marked as unsupported, >>>>>> efibootmgr will just exit on efi_variables_supported() check [1] in >>>>>> a way that its parent process, i.e. grub-install, doesn't take as an >>>>>> error. But otherwise, efibootmgr will go much further and exit with >>>>>> a real error when trying to access efivars. >>>>>> >>>>> >>>>> OK, so I suggest we fix efibootmgr, by extending the >>>>> efi_variables_supported() check to perform a GetVariable() call on an >>>>> arbitrary variable (e.g., BootOrder), >>>> >>>> Hmm, I'm not sure we should ask more from user space, as it's already >>>> been doing the right thing, and efi_variables_supported() is proved to >>>> work properly with any sane low-level software (kernel + firmware), >>>> either EFI variables service is supported or not. That said, IMHO, >> >> No, there is not one but there are three EFI variable services. >> >> GetVariable() available after ExitBootServices() and SetVariable() not >> available() is completely legal according to the current UEFI specification. >> > > This is a valid point. efibootmgr may be able to read the Boot#### > variables, but may be unable to change them. > >>>> right now the low-level software on Snapdragon laptops is insane, i.e. >>>> the unsupported/broken EFI runtime services are not communicated to >>>> user space properly in established way. >> >> Please, describe: >> >> * Which UEFI version is reported by your Snapdragon laptop? >> * What is the observed behavior? >> > > These laptops have the EFI varstore in a eMMC partition. This is > basically the same problem that many uboot based platforms have as > well, i.e., that it is not possible for the OS and the firmware to > share the MMC because the ownership of the MMC controller cannot be > shared. > >>> >>> But the EFI_UNSUPPORTED is an error that's allowed from the spec. >>> Yes the sane thing to do is not expose it at all, but it's not violating >>> any spec by doing so. >>> So why shouldn't a userspace application be able to handle all return codes >>> explicitly and instead treat them as a single error? And when that happens why >>> shouldut the kernel mask that error out for it? >> >> The runtime services must always be callable even they can only report >> EFI_UNSUPPORTED. >> >> Only since UEFI specification 2.8 errata B do we have the >> EFI_RT_PROPERTIES_TABLE which tells us which runtime services are >> implemented. >> >> UEFI 2.8 B makes it clear that any runtime service may be reported as >> unsupported. EFI applications are expected to cope with a service being >> unavailable. >> > > Indeed. The firmware on these machines predates the UEFI 2.8B > specification, but given the fact that EFI_UNSUPPORTED is a valid > return code now for these services, we should deal with them > gracefully anyway. And apparently, doing so would also remove the need > for special hacks to support installing GRUB on these platforms. > Hello Ard, it is still unclear to why you would need the patch. Why should a user provide a UEFI variable telling which service is not working correctly? Is the firmware correctly returning EFI_UNSUPPORTED for unsupported services? For which services? In which software is the bug that cannot gracefully deal with unsupported services? GRUB never gave me a problem on boards with U-Boot which only provides GetVariable() and not SetVariable(). GRUB spits out warnings but works as expected. Best regards Heinrich
