Re: [PATCH v2 1/2] efi/arm: decompressor: deal with HYP mode boot gracefully

[Ard Biesheuvel <ardb@kernel.org>]

On Mon, 8 Jun 2020 at 12:46, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>
> On 6/8/20 1:08 AM, Ard Biesheuvel wrote:
> > On Sun, 7 Jun 2020 at 19:24, Heinrich Schuchardt <xypron.glpk@gmx.de> 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@gmx.de>
>
> 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?


> EFI stub: Booting Linux Kernel...
> EFI stub: ERROR: Could not determine UEFI Secure Boot status.
> EFI stub: Using DTB from configuration table
> EFI stub: Exiting boot services and installing virtual address map...
> EHCI failed to shut down host controller.
> [    0.000000] Booting Linux on physical CPU 0x0
> [    0.000000] Linux version 5.7.0-armmp-lpae+ (user@node)
> (arm-linux-gnueabihf-gcc (Debian 9.3.0-13) 9.3.0, GNU ld (GNU Binutils
> for Debian) 2.34) #10 SMP Mon Jun 8 03:44:37 CEST 2020
> [    0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7),
> cr=30c5387d
> [    0.000000] CPU: div instructions available: patching division code
> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing
> instruction cache
> [    0.000000] OF: fdt: Machine model: Xunlong Orange Pi PC
> [    0.000000] Memory policy: Data cache writealloc
> [    0.000000] efi: EFI v2.80 by Das U-Boot
> [    0.000000] efi: RTPROP=0x78f30040 SMBIOS=0x78f2a000
> MEMRESERVE=0x6a1fa040
> [    0.000000] cma: Reserved 16 MiB at 0x000000007f000000
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000040000000-0x000000006fffffff]
> [    0.000000]   Normal   empty
> [    0.000000]   HighMem  [mem 0x0000000070000000-0x000000007fffffff]
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000078f07fff]
> [    0.000000]   node   0: [mem 0x0000000078f08000-0x0000000078f09fff]
> [    0.000000]   node   0: [mem 0x0000000078f0a000-0x0000000078f24fff]
> [    0.000000]   node   0: [mem 0x0000000078f25000-0x0000000078f28fff]
> [    0.000000]   node   0: [mem 0x0000000078f29000-0x0000000078f29fff]
> [    0.000000]   node   0: [mem 0x0000000078f2a000-0x0000000078f2afff]
> [    0.000000]   node   0: [mem 0x0000000078f2b000-0x0000000078f2cfff]
> [    0.000000]   node   0: [mem 0x0000000078f2d000-0x0000000078f2dfff]
> [    0.000000]   node   0: [mem 0x0000000078f2e000-0x0000000078f2ffff]
> [    0.000000]   node   0: [mem 0x0000000078f30000-0x0000000078f32fff]
> [    0.000000]   node   0: [mem 0x0000000078f33000-0x0000000078f33fff]
> [    0.000000]   node   0: [mem 0x0000000078f34000-0x0000000078f34fff]
> [    0.000000]   node   0: [mem 0x0000000078f35000-0x0000000078f35fff]
> [    0.000000]   node   0: [mem 0x0000000078f36000-0x0000000078f36fff]
> [    0.000000]   node   0: [mem 0x0000000078f37000-0x0000000078f38fff]
> [    0.000000]   node   0: [mem 0x0000000078f39000-0x0000000078f3efff]
> [    0.000000]   node   0: [mem 0x0000000078f3f000-0x000000007df65fff]
> [    0.000000]   node   0: [mem 0x000000007df66000-0x000000007df66fff]
> [    0.000000]   node   0: [mem 0x000000007df67000-0x000000007dfb9fff]
> [    0.000000]   node   0: [mem 0x000000007dfba000-0x000000007dfbcfff]
> [    0.000000]   node   0: [mem 0x000000007dfbd000-0x000000007fffffff]
> [    0.000000] Initmem setup node 0 [mem
> 0x0000000040000000-0x000000007fffffff]
> [    0.000000] psci: probing for conduit method from DT.
> [    0.000000] psci: Using PSCI v0.1 Function IDs from DT