On Thu, Aug 15, 2024 at 10:39 PM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
>
> With the latest Linux-6.11-rc3, the below NULL pointer crash is observed
> when SBI PMU snapshot is enabled for the guest and the guest is forcefully
> powered-off.
>
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000508
> Oops [#1]
> Modules linked in: kvm
> CPU: 0 UID: 0 PID: 61 Comm: term-poll Not tainted 6.11.0-rc3-00018-g44d7178dd77a #3
> Hardware name: riscv-virtio,qemu (DT)
> epc : __kvm_write_guest_page+0x94/0xa6 [kvm]
> ra : __kvm_write_guest_page+0x54/0xa6 [kvm]
> epc : ffffffff01590e98 ra : ffffffff01590e58 sp : ffff8f80001f39b0
> gp : ffffffff81512a60 tp : ffffaf80024872c0 t0 : ffffaf800247e000
> t1 : 00000000000007e0 t2 : 0000000000000000 s0 : ffff8f80001f39f0
> s1 : 00007fff89ac4000 a0 : ffffffff015dd7e8 a1 : 0000000000000086
> a2 : 0000000000000000 a3 : ffffaf8000000000 a4 : ffffaf80024882c0
> a5 : 0000000000000000 a6 : ffffaf800328d780 a7 : 00000000000001cc
> s2 : ffffaf800197bd00 s3 : 00000000000828c4 s4 : ffffaf800248c000
> s5 : ffffaf800247d000 s6 : 0000000000001000 s7 : 0000000000001000
> s8 : 0000000000000000 s9 : 00007fff861fd500 s10: 0000000000000001
> s11: 0000000000800000 t3 : 00000000000004d3 t4 : 00000000000004d3
> t5 : ffffffff814126e0 t6 : ffffffff81412700
> status: 0000000200000120 badaddr: 0000000000000508 cause: 000000000000000d
> [<ffffffff01590e98>] __kvm_write_guest_page+0x94/0xa6 [kvm]
> [<ffffffff015943a6>] kvm_vcpu_write_guest+0x56/0x90 [kvm]
> [<ffffffff015a175c>] kvm_pmu_clear_snapshot_area+0x42/0x7e [kvm]
> [<ffffffff015a1972>] kvm_riscv_vcpu_pmu_deinit.part.0+0xe0/0x14e [kvm]
> [<ffffffff015a2ad0>] kvm_riscv_vcpu_pmu_deinit+0x1a/0x24 [kvm]
> [<ffffffff0159b344>] kvm_arch_vcpu_destroy+0x28/0x4c [kvm]
> [<ffffffff0158e420>] kvm_destroy_vcpus+0x5a/0xda [kvm]
> [<ffffffff0159930c>] kvm_arch_destroy_vm+0x14/0x28 [kvm]
> [<ffffffff01593260>] kvm_destroy_vm+0x168/0x2a0 [kvm]
> [<ffffffff015933d4>] kvm_put_kvm+0x3c/0x58 [kvm]
> [<ffffffff01593412>] kvm_vm_release+0x22/0x2e [kvm]
>
> Clearly, the kvm_vcpu_write_guest() function is crashing because it is
> being called from kvm_pmu_clear_snapshot_area() upon guest tear down.
>
> To address the above issue, simplify the kvm_pmu_clear_snapshot_area() to
> not zero-out PMU snapshot area from kvm_pmu_clear_snapshot_area() because
> the guest is anyway being tore down.
>
> The kvm_pmu_clear_snapshot_area() is also called when guest changes
> PMU snapshot area of a VCPU but even in this case the previous PMU
> snaphsot area must not be zeroed-out because the guest might have
> reclaimed the pervious PMU snapshot area for some other purpose.
>
> Fixes: c2f41ddbcdd7 ("RISC-V: KVM: Implement SBI PMU Snapshot feature")
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
Queued this patch for Linux-6.11 fixes.
Regards,
Anup
> ---
> arch/riscv/kvm/vcpu_pmu.c | 14 ++------------
> 1 file changed, 2 insertions(+), 12 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index bcf41d6e0df0..2707a51b082c 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -391,19 +391,9 @@ int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
> static void kvm_pmu_clear_snapshot_area(struct kvm_vcpu *vcpu)
> {
> struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> - int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
>
> - if (kvpmu->sdata) {
> - if (kvpmu->snapshot_addr != INVALID_GPA) {
> - memset(kvpmu->sdata, 0, snapshot_area_size);
> - kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr,
> - kvpmu->sdata, snapshot_area_size);
> - } else {
> - pr_warn("snapshot address invalid\n");
> - }
> - kfree(kvpmu->sdata);
> - kvpmu->sdata = NULL;
> - }
> + kfree(kvpmu->sdata);
> + kvpmu->sdata = NULL;
> kvpmu->snapshot_addr = INVALID_GPA;
> }
>
> --
> 2.34.1
>
