[PATCH] kvm-arm: Unmap shadow pagetables properly

Suzuki K Poulose
2016-09-08T15:26:02Z

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().

Reported-by: Itaru Kitayama <itaru.kitayama@riken.jp>
Reported-by: James 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: Suzuki K Poulose <suzuki.poulose@arm.com>
---
arch/arm/kvm/arm.c | 2 --
arch/arm/kvm/mmu.c | 1 +
2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 75f130e..c94b90d 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -158,8 +158,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
{
int i;

- kvm_free_stage2_pgd(kvm);
-
for (i = 0; i < KVM_MAX_VCPUS; ++i) {
if (kvm->vcpus[i]) {
kvm_arch_vcpu_free(kvm->vcpus[i]);
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 29d0b23..d626d08 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1893,6 +1893,7 @@ void kvm_arch_memslots_updated(struct kvm *kvm, struct kvm_memslots *slots)

void kvm_arch_flush_shadow_all(struct kvm *kvm)
{
+ kvm_free_stage2_pgd(kvm);
}

void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
--
2.7.4