On Tue, Jun 23, 2020 at 06:59:36PM +0200, Ard Biesheuvel wrote:
> Commit
>
> 84e6ffb2c49c7901 ("arm: add support for folded p4d page tables")
>
> updated create_mapping_late() to take folded P4Ds into account when
> creating mappings, but inverted the p4d_alloc() failure test, resulting
> in no mapping to be created at all.
>
> When the EFI rtc driver subsequently tries to invoke the EFI GetTime()
> service, the memory regions covering the EFI data structures are missing
> from the page tables, resulting in a crash like
>
> Unable to handle kernel paging request at virtual address 5ae0cf28
> pgd = (ptrval)
> [5ae0cf28] *pgd=80000040205003, *pmd=00000000
> Internal error: Oops: 207 [#1] SMP THUMB2
> Modules linked in:
> CPU: 0 PID: 7 Comm: kworker/u32:0 Not tainted 5.7.0+ #92
> Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> Workqueue: efi_rts_wq efi_call_rts
> PC is at efi_call_rts+0x94/0x294
> LR is at efi_call_rts+0x83/0x294
> pc : [<c0b4f098>] lr : [<c0b4f087>] psr: 30000033
> sp : e6219ef0 ip : 00000000 fp : ffffe000
> r10: 00000000 r9 : 00000000 r8 : 30000013
> r7 : e6201dd0 r6 : e6201ddc r5 : 00000000 r4 : c181f264
> r3 : 5ae0cf10 r2 : 00000001 r1 : e6201dd0 r0 : e6201ddc
> Flags: nzCV IRQs on FIQs on Mode SVC_32 ISA Thumb Segment none
> Control: 70c5383d Table: 661cc840 DAC: 00000001
> Process kworker/u32:0 (pid: 7, stack limit = 0x(ptrval))
> ...
> [<c0b4f098>] (efi_call_rts) from [<c0448219>] (process_one_work+0x16d/0x3d8)
> [<c0448219>] (process_one_work) from [<c0448581>] (worker_thread+0xfd/0x408)
> [<c0448581>] (worker_thread) from [<c044ca7b>] (kthread+0x103/0x104)
> ...
>
> Fixes: 84e6ffb2c49c7901 ("arm: add support for folded p4d page tables")
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> arch/arm/mm/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 628028bfbb92..bcd82614c25d 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -966,7 +966,7 @@ void __init create_mapping_late(struct mm_struct *mm, struct map_desc *md,
> pud_t *pud;
>
> p4d = p4d_alloc(mm, pgd_offset(mm, md->virtual), md->virtual);
> - if (!WARN_ON(!p4d))
> + if (WARN_ON(!p4d))
It must have been cosmic radiation :)
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> return;
> pud = pud_alloc(mm, p4d, md->virtual);
> if (WARN_ON(!pud))
> --
> 2.27.0
>
--
Sincerely yours,
Mike.
