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linux/arch/arm/kvm
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Marc Zyngier f75e09ebd3 KVM: arm/arm64: Handle possible NULL stage2 pud when ageing pages 
commit d6dbdd3c85 upstream.

Under memory pressure, we start ageing pages, which amounts to parsing
the page tables. Since we don't want to allocate any extra level,
we pass NULL for our private allocation cache. Which means that
stage2_get_pud() is allowed to fail. This results in the following
splat:

[ 1520.409577] Unable to handle kernel NULL pointer dereference at virtual address 00000008
[ 1520.417741] pgd = ffff810f52fef000
[ 1520.421201] [00000008] *pgd=0000010f636c5003, *pud=0000010f56f48003, *pmd=0000000000000000
[ 1520.429546] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[ 1520.435156] Modules linked in:
[ 1520.438246] CPU: 15 PID: 53550 Comm: qemu-system-aar Tainted: G        W       4.12.0-rc4-00027-g1885c397eaec #7205
[ 1520.448705] Hardware name: FOXCONN R2-1221R-A4/C2U4N_MB, BIOS G31FB12A 10/26/2016
[ 1520.463726] task: ffff800ac5fb4e00 task.stack: ffff800ce04e0000
[ 1520.469666] PC is at stage2_get_pmd+0x34/0x110
[ 1520.474119] LR is at kvm_age_hva_handler+0x44/0xf0
[ 1520.478917] pc : [<ffff0000080b137c>] lr : [<ffff0000080b149c>] pstate: 40000145
[ 1520.486325] sp : ffff800ce04e33d0
[ 1520.489644] x29: ffff800ce04e33d0 x28: 0000000ffff40064
[ 1520.494967] x27: 0000ffff27e00000 x26: 0000000000000000
[ 1520.500289] x25: ffff81051ba65008 x24: 0000ffff40065000
[ 1520.505618] x23: 0000ffff40064000 x22: 0000000000000000
[ 1520.510947] x21: ffff810f52b20000 x20: 0000000000000000
[ 1520.516274] x19: 0000000058264000 x18: 0000000000000000
[ 1520.521603] x17: 0000ffffa6fe7438 x16: ffff000008278b70
[ 1520.526940] x15: 000028ccd8000000 x14: 0000000000000008
[ 1520.532264] x13: ffff7e0018298000 x12: 0000000000000002
[ 1520.537582] x11: ffff000009241b93 x10: 0000000000000940
[ 1520.542908] x9 : ffff0000092ef800 x8 : 0000000000000200
[ 1520.548229] x7 : ffff800ce04e36a8 x6 : 0000000000000000
[ 1520.553552] x5 : 0000000000000001 x4 : 0000000000000000
[ 1520.558873] x3 : 0000000000000000 x2 : 0000000000000008
[ 1520.571696] x1 : ffff000008fd5000 x0 : ffff0000080b149c
[ 1520.577039] Process qemu-system-aar (pid: 53550, stack limit = 0xffff800ce04e0000)
[...]
[ 1521.510735] [<ffff0000080b137c>] stage2_get_pmd+0x34/0x110
[ 1521.516221] [<ffff0000080b149c>] kvm_age_hva_handler+0x44/0xf0
[ 1521.522054] [<ffff0000080b0610>] handle_hva_to_gpa+0xb8/0xe8
[ 1521.527716] [<ffff0000080b3434>] kvm_age_hva+0x44/0xf0
[ 1521.532854] [<ffff0000080a58b0>] kvm_mmu_notifier_clear_flush_young+0x70/0xc0
[ 1521.539992] [<ffff000008238378>] __mmu_notifier_clear_flush_young+0x88/0xd0
[ 1521.546958] [<ffff00000821eca0>] page_referenced_one+0xf0/0x188
[ 1521.552881] [<ffff00000821f36c>] rmap_walk_anon+0xec/0x250
[ 1521.558370] [<ffff000008220f78>] rmap_walk+0x78/0xa0
[ 1521.563337] [<ffff000008221104>] page_referenced+0x164/0x180
[ 1521.569002] [<ffff0000081f1af0>] shrink_active_list+0x178/0x3b8
[ 1521.574922] [<ffff0000081f2058>] shrink_node_memcg+0x328/0x600
[ 1521.580758] [<ffff0000081f23f4>] shrink_node+0xc4/0x328
[ 1521.585986] [<ffff0000081f2718>] do_try_to_free_pages+0xc0/0x340
[ 1521.592000] [<ffff0000081f2a64>] try_to_free_pages+0xcc/0x240
[...]

The trivial fix is to handle this NULL pud value early, rather than
dereferencing it blindly.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2017-06-14 15:06:02 +02:00
..
hyp KVM: arm: plug potential guest hardware debug leakage 2017-05-25 15:44:44 +02:00
arm.c arm/arm64: KVM: Perform local TLB invalidation when multiplexing vcpus on a single CPU 2016-11-04 17:56:28 +00:00
coproc.c KVM: arm: plug potential guest hardware debug leakage 2017-05-25 15:44:44 +02:00
coproc.h ARM: KVM: Rename struct coproc_reg::is_64 to is_64bit 2016-02-29 18:34:22 +00:00
coproc_a7.c arm/arm64: KVM: Use set/way op trapping to track the state of the caches 2015-01-29 23:24:56 +01:00
coproc_a15.c arm/arm64: KVM: Use set/way op trapping to track the state of the caches 2015-01-29 23:24:56 +01:00
emulate.c arm: KVM: Add Virtual Abort injection helper 2016-09-08 12:53:00 +02:00
guest.c KVM: ARM: Fix typos 2016-06-14 11:16:26 +02:00
handle_exit.c KVM: arm: plug potential guest hardware debug leakage 2017-05-25 15:44:44 +02:00
init.S arm: KVM: Allow unaligned accesses at HYP 2017-06-14 15:05:56 +02:00
interrupts.S ARM: KVM: Remove the old world switch 2016-02-29 18:34:14 +00:00
irq.h KVM: arm/arm64: Enable irqchip routing 2016-07-22 18:52:01 +01:00
Kconfig KVM: arm/arm64: Enable irqchip routing 2016-07-22 18:52:01 +01:00
Makefile ARM: KVM: Support vgic-v3 2016-09-22 13:22:21 +02:00
mmio.c arm/arm64: KVM: Remove external abort test from MMIO handling 2016-09-08 12:53:00 +02:00
mmu.c KVM: arm/arm64: Handle possible NULL stage2 pud when ageing pages 2017-06-14 15:06:02 +02:00
perf.c ARM: KVM: add support for minimal host vs guest profiling 2013-04-28 21:44:01 -07:00
psci.c KVM: arm/arm64: fix races in kvm_psci_vcpu_on 2017-05-20 14:28:36 +02:00
reset.c KVM: ARM: Fix typos 2016-06-14 11:16:26 +02:00
trace.h arm/arm64: KVM: Improve kvm_exit tracepoint 2015-10-22 23:01:47 +02:00