• Suzuki K Poulose's avatar
    kvm-arm: Unmap shadow pagetables properly · 293f2936
    Suzuki K Poulose authored
    On arm/arm64, we depend on the kvm_unmap_hva* callbacks (via
    mmu_notifiers::invalidate_*) to unmap the stage2 pagetables when
    the userspace buffer gets unmapped. However, when the Hypervisor
    process exits without explicit unmap of the guest buffers, the only
    notifier we get is kvm_arch_flush_shadow_all() (via mmu_notifier::release
    ) which does nothing on arm. Later this causes us to access pages that
    were already released [via exit_mmap() -> unmap_vmas()] when we actually
    get to unmap the stage2 pagetable [via kvm_arch_destroy_vm() ->
    kvm_free_stage2_pgd()]. This triggers crashes with CONFIG_DEBUG_PAGEALLOC,
    which unmaps any free'd pages from the linear map.
    
     [  757.644120] Unable to handle kernel paging request at virtual address
      ffff800661e00000
     [  757.652046] pgd = ffff20000b1a2000
     [  757.655471] [ffff800661e00000] *pgd=00000047fffe3003, *pud=00000047fcd8c003,
      *pmd=00000047fcc7c003, *pte=00e8004661e00712
     [  757.666492] Internal error: Oops: 96000147 [#3] PREEMPT SMP
     [  757.672041] Modules linked in:
     [  757.675100] CPU: 7 PID: 3630 Comm: qemu-system-aar Tainted: G      D
     4.8.0-rc1 #3
     [  757.683240] Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board,
      BIOS 3.06.15 Aug 19 2016
     [  757.692938] task: ffff80069cdd3580 task.stack: ffff8006adb7c000
     [  757.698840] PC is at __flush_dcache_area+0x1c/0x40
     [  757.703613] LR is at kvm_flush_dcache_pmd+0x60/0x70
     [  757.708469] pc : [<ffff20000809dbdc>] lr : [<ffff2000080b4a70>] pstate: 20000145
     ...
     [  758.357249] [<ffff20000809dbdc>] __flush_dcache_area+0x1c/0x40
     [  758.363059] [<ffff2000080b6748>] unmap_stage2_range+0x458/0x5f0
     [  758.368954] [<ffff2000080b708c>] kvm_free_stage2_pgd+0x34/0x60
     [  758.374761] [<ffff2000080b2280>] kvm_arch_destroy_vm+0x20/0x68
     [  758.380570] [<ffff2000080aa330>] kvm_put_kvm+0x210/0x358
     [  758.385860] [<ffff2000080aa524>] kvm_vm_release+0x2c/0x40
     [  758.391239] [<ffff2000082ad234>] __fput+0x114/0x2e8
     [  758.396096] [<ffff2000082ad46c>] ____fput+0xc/0x18
     [  758.400869] [<ffff200008104658>] task_work_run+0x108/0x138
     [  758.406332] [<ffff2000080dc8ec>] do_exit+0x48c/0x10e8
     [  758.411363] [<ffff2000080dd5fc>] do_group_exit+0x6c/0x130
     [  758.416739] [<ffff2000080ed924>] get_signal+0x284/0xa18
     [  758.421943] [<ffff20000808a098>] do_signal+0x158/0x860
     [  758.427060] [<ffff20000808aad4>] do_notify_resume+0x6c/0x88
     [  758.432608] [<ffff200008083624>] work_pending+0x10/0x14
     [  758.437812] Code: 9ac32042 8b010001 d1000443 8a230000 (d50b7e20)
    
    This patch fixes the issue by moving the kvm_free_stage2_pgd() to
    kvm_arch_flush_shadow_all().
    
    Cc: <stable@vger.kernel.org> # 3.9+
    Tested-by: default avatarItaru Kitayama <itaru.kitayama@riken.jp>
    Reported-by: default avatarItaru Kitayama <itaru.kitayama@riken.jp>
    Reported-by: default avatarJames Morse <james.morse@arm.com>
    Cc: Marc Zyngier <marc.zyngier@arm.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Christoffer Dall <christoffer.dall@linaro.org>
    Signed-off-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
    Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
    293f2936
mmu.c 51.7 KB