On Tue, 9 Jun 2020 at 09:58, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > On Mon, 8 Jun 2020 at 12:46, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: > > > > On 6/8/20 1:08 AM, Ard Biesheuvel wrote: > > > On Sun, 7 Jun 2020 at 19:24, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: > > >> > > >> On 6/7/20 3:58 PM, Ard Biesheuvel wrote: > > >>> EFI on ARM only supports short descriptors, and given that it mandates > > >>> that the MMU and caches are on, it is implied that booting in HYP mode > > >>> is not supported. > > >>> > > >>> However, implementations of EFI exist (i.e., U-Boot) that ignore this > > >>> requirement, which is not entirely unreasonable, given that it makes > > >>> HYP mode inaccessible to the operating system. > > >>> > > >>> So let's make sure that we can deal with this condition gracefully. > > >>> We already tolerate booting the EFI stub with the caches off (even > > >>> though this violates the EFI spec as well), and so we should deal > > >>> with HYP mode boot with MMU and caches either on or off. > > >>> > > >>> - When the MMU and caches are on, we can ignore the HYP stub altogether, > > >>> since we can carry on executing at HYP. We do need to ensure that we > > >>> disable the MMU at HYP before entering the kernel proper. > > >>> > > >>> - When the MMU and caches are off, we have to drop to SVC mode so that > > >>> we can set up the page tables using short descriptors. In this case, > > >>> we need to install the HYP stub as usual, so that we can return to HYP > > >>> mode before handing over to the kernel proper. > ... > > > > Hello Ard, > > > > thanks for supplying a branch for testing: > > https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=efi-arm-hyp-mode > > > > The OrangePi PC boots fine with this branch. PSCI is enabled. Rebooting > > the system works fine. See log below. > > > > With the patch 2/2 you add an output line for the exceptions level and > > the MMU status. Above you state "We already tolerate booting the EFI > > stub with the caches off." This relates to a workaround in U-Boot > > accomodating old GRUB versions (CONFIG_EFI_GRUB_ARM32_WORKAROUND=y). > > > > Would a further diagnostic line showing if D-cache and I-cache is > > enabled make sense? > > > > Tested-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> > > > > Loading Linux 5.7.0-armmp-lpae+ ... > > Loading initial ramdisk ... > > EFI stub: Running in HYP mode with MMU enabled > > BTW is this with or without the GRUB hack? > I've given this a spin myself on a RPi4 running 32-bit U-boot, and everything works as expected, both with and without the GRUB hack enabled. Russell, given that this only affects code inside #ifdef CONFIG_EFI_STUB, do you have any objections to me taking this as a fix via the EFI tree? I have a set of fixes I need to queue up and send out anyway, and I intend to do so early next week.
