[Possible BUG] arm64: efi: efi_runtime_fixup_exception() and efi_call_virt_check_flags() both taint the kernel

[Alexandru Elisei]

I'm going to preface this by saying that I'm extremely unfamiliar with the
EFI code.

Commit d3549a938b73 ("efi/arm64: libstub: avoid SetVirtualAddressMap() when
possible") skipped the call to SetVirtualAddressMap() for certain
configurations, and that started causing kernel panics on an Ampere Altra
machine due to an EFI synchronous exception.

Commit 23715a26c8d8 ("arm64: efi: Recover from synchronous exceptions
occurring in firmware") made the EFI exception non-fatal.

With a kernel built from v6.1-rc4 (which has both patches), I'm now getting
two splats on the same Altra machine (log below). Looks to me like the
second splat is caused by efi_call_virt_check_flags() using the
PSTATE.{I,F} values from when taking the exception. Shouldn't
efi_runtime_fixup_exception() fix up the exception so the error isn't
propagated along the call chain?

I'm asking this because efi_runtime_fixup_exception() has this add_taint()
call:

	pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg);
	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);

and then efi_call_virt_check_flags() has this call:

        mismatch = flags ^ cur_flags;
        if (!WARN_ON_ONCE(mismatch & ARCH_EFI_IRQ_FLAGS_MASK))
                return;

        add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_NOW_UNRELIABLE);

It looks to me like LOCKDEP_STILL_OK from the first call is at odds with
LOCKDEP_NOW_UNRELIABLE from the second add_taint() call.

Here is the relevant part of the log (I can send the .config, kernel
command line and full log, or any other information that might be needed):

[   55.479519] [Firmware Bug]: Unable to handle paging request in EFI runtime service
[   55.487122] CPU: 62 PID: 9 Comm: kworker/u320:0 Tainted: G          I        6.1.0-rc4 #60
[   55.487128] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
[   55.487131] Workqueue: efi_rts_wq efi_call_rts
[   55.487158] Call trace:
[   55.487161]  dump_backtrace.part.0+0xdc/0xf0
[   55.487177]  show_stack+0x18/0x40
[   55.487180]  dump_stack_lvl+0x68/0x84
[   55.487190]  dump_stack+0x18/0x34
[   55.487192]  efi_runtime_fixup_exception+0x74/0x88
[   55.487199]  __do_kernel_fault+0x108/0x1b0
[   55.487204]  do_page_fault+0xd0/0x400
[   55.487207]  do_translation_fault+0xac/0xc0
[   55.487209]  do_mem_abort+0x44/0x94
[   55.487212]  el1_abort+0x40/0x6c
[   55.487214]  el1h_64_sync_handler+0xd8/0xe4
[   55.487218]  el1h_64_sync+0x64/0x68
[   55.487221]  0xb7eb7ae4
[   55.487224]  0xb7eb8668
[   55.487225]  0xb7eb6e08
[   55.487227]  0xb7eb68ec
[   55.487228]  0xb7eb3824
[   55.487230]  0xb7eb05a8
[   55.487231]  0xb7eb12a0
[   55.487232]  0xb7e43504
[   55.487234]  0xb7e43650
[   55.487235]  0xb7e482d0
[   55.487237]  0xb7e4907c
[   55.487238]  0xb7e49ff4
[   55.487239]  0xb7e40888
[   55.487241]  0xb7cb3328
[   55.487242]  0xb7cb0674
[   55.487243]  __efi_rt_asm_wrapper+0x54/0x70
[   55.487246]  efi_call_rts+0x28c/0x3d0
[   55.487249]  process_one_work+0x1d0/0x320
[   55.487258]  worker_thread+0x14c/0x444
[   55.487261]  kthread+0x10c/0x110
[   55.487264]  ret_from_fork+0x10/0x20
[   55.487268] [Firmware Bug]: Synchronous exception occurred in EFI runtime service set_time()
[   55.495735] ------------[ cut here ]------------
[   55.495739] WARNING: CPU: 62 PID: 9 at drivers/firmware/efi/runtime-wrappers.c:111 efi_call_virt_check_flags+0x40/0xac
[   55.495746] Modules linked in:
[   55.495749] CPU: 62 PID: 9 Comm: kworker/u320:0 Tainted: G          I        6.1.0-rc4 #60
[   55.495751] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
[   55.495753] Workqueue: efi_rts_wq efi_call_rts
[   55.495757] pstate: 004000c9 (nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   55.495761] pc : efi_call_virt_check_flags+0x40/0xac
[   55.495764] lr : efi_call_rts+0x29c/0x3d0
[   55.495767] sp : ffff80000861bd40
[   55.495768] x29: ffff80000861bd40 x28: 0000000000000000 x27: 0000000000000000
[   55.495772] x26: ffffb251470e9e68 x25: ffff3fff89714805 x24: 0000000000000000
[   55.495775] x23: 0000000000000000 x22: 0000000000000000 x21: 00000000000000c0
[   55.495778] x20: ffffb25146688de0 x19: 0000000000000000 x18: ffffffffffffffff
[   55.495780] x17: 657320656d69746e x16: 757220494645206e x15: 6920646572727563
[   55.495784] x14: 636f206e6f697470 x13: ffff403e40540000 x12: 0000000000001c14
[   55.495787] x11: 000000000000095c x10: ffff403e40800000 x9 : ffff403e40540000
[   55.495790] x8 : 00000000ffff7fff x7 : ffff403e40800000 x6 : 0000000000000000
[   55.495792] x5 : ffff083e7fe9aaa0 x4 : 0000000000000000 x3 : 0000000000000000
[   55.495796] x2 : 0000000000000000 x1 : ffffb25146688de0 x0 : 00000000000000c0
[   55.495799] Call trace:
[   55.495800]  efi_call_virt_check_flags+0x40/0xac
[   55.495802]  efi_call_rts+0x29c/0x3d0
[   55.495805]  process_one_work+0x1d0/0x320
[   55.495808]  worker_thread+0x14c/0x444
[   55.495811]  kthread+0x10c/0x110
[   55.495814]  ret_from_fork+0x10/0x20
[   55.495815] ---[ end trace 0000000000000000 ]---
[   55.495818] Disabling lock debugging due to kernel taint
[   55.495822] efi: [Firmware Bug]: IRQ flags corrupted (0x00000000=>0x000000c0) by EFI set_time
[   55.504434] efi: EFI Runtime Services are disabled!
[   55.504465] rtc-efi rtc-efi.0: can't read time
[   56.479370] efi: EFI Runtime Services are disabled!
[   56.479394] rtc-efi rtc-efi.0: can't read time
[   57.479574] rtc-efi rtc-efi.0: can't read time
[   57.484030] rtc-efi rtc-efi.0: can't read time
[   57.488474] rtc-efi rtc-efi.0: can't read time
[   58.479692] rtc-efi rtc-efi.0: can't read time
[   58.484139] rtc-efi rtc-efi.0: can't read time

(rtc-efi error message repeats ad nauseum)

Note: this error message from the EFI rtc driver fires over and over and
clutters dmesg, will send a different report for this as I don't think it's
necessarily related to the two functions.

Thanks,
Alex