Re: [PATCH v5 3/3] KVM: nVMX: Fix mmu context after VMLAUNCH/VMRESUME failure

[Jim Mattson <jmattson@google.com>]

That seems reasonable to me. Thanks for the fix.

Reviewed-by: Jim Mattson <jmattson@google.com>

On Thu, Nov 2, 2017 at 5:50 PM, Wanpeng Li <kernellwp@gmail.com> wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> Commit 4f350c6dbcb (kvm: nVMX: Handle deferred early VMLAUNCH/VMRESUME failure
> properly) can result in L1(run kvm-unit-tests/run_tests.sh vmx_controls in L1)
> null pointer deference and also L0 calltrace when EPT=0 on both L0 and L1.
>
> In L1:
>
> BUG: unable to handle kernel paging request at ffffffffc015bf8f
>  IP: vmx_vcpu_run+0x202/0x510 [kvm_intel]
>  PGD 146e13067 P4D 146e13067 PUD 146e15067 PMD 3d2686067 PTE 3d4af9161
>  Oops: 0003 [#1] PREEMPT SMP
>  CPU: 2 PID: 1798 Comm: qemu-system-x86 Not tainted 4.14.0-rc4+ #6
>  RIP: 0010:vmx_vcpu_run+0x202/0x510 [kvm_intel]
>  Call Trace:
>  WARNING: kernel stack frame pointer at ffffb86f4988bc18 in qemu-system-x86:1798 has bad value 0000000000000002
>
> In L0:
>
> -----------[ cut here ]------------
>  WARNING: CPU: 6 PID: 4460 at /home/kernel/linux/arch/x86/kvm//vmx.c:9845 vmx_inject_page_fault_nested+0x130/0x140 [kvm_intel]
>  CPU: 6 PID: 4460 Comm: qemu-system-x86 Tainted: G           OE   4.14.0-rc7+ #25
>  RIP: 0010:vmx_inject_page_fault_nested+0x130/0x140 [kvm_intel]
>  Call Trace:
>   paging64_page_fault+0x500/0xde0 [kvm]
>   ? paging32_gva_to_gpa_nested+0x120/0x120 [kvm]
>   ? nonpaging_page_fault+0x3b0/0x3b0 [kvm]
>   ? __asan_storeN+0x12/0x20
>   ? paging64_gva_to_gpa+0xb0/0x120 [kvm]
>   ? paging64_walk_addr_generic+0x11a0/0x11a0 [kvm]
>   ? lock_acquire+0x2c0/0x2c0
>   ? vmx_read_guest_seg_ar+0x97/0x100 [kvm_intel]
>   ? vmx_get_segment+0x2a6/0x310 [kvm_intel]
>   ? sched_clock+0x1f/0x30
>   ? check_chain_key+0x137/0x1e0
>   ? __lock_acquire+0x83c/0x2420
>   ? kvm_multiple_exception+0xf2/0x220 [kvm]
>   ? debug_check_no_locks_freed+0x240/0x240
>   ? debug_smp_processor_id+0x17/0x20
>   ? __lock_is_held+0x9e/0x100
>   kvm_mmu_page_fault+0x90/0x180 [kvm]
>   kvm_handle_page_fault+0x15c/0x310 [kvm]
>   ? __lock_is_held+0x9e/0x100
>   handle_exception+0x3c7/0x4d0 [kvm_intel]
>   vmx_handle_exit+0x103/0x1010 [kvm_intel]
>   ? kvm_arch_vcpu_ioctl_run+0x1628/0x2e20 [kvm]
>
> The commit avoids to load host state of vmcs12 as vmcs01's guest state
> since vmcs12 is not modified (except for the VM-instruction error field)
> if the checking of vmcs control area fails. However, the mmu context is
> switched to nested mmu in prepare_vmcs02() and it will not be reloaded
> since load_vmcs12_host_state() is skipped when nested VMLAUNCH/VMRESUME
> fails. This patch fixes it by reloading mmu context when nested
> VMLAUNCH/VMRESUME fails.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Jim Mattson <jmattson@google.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> v3 -> v4:
>  * move it to a new function load_vmcs12_mmu_host_state
>
>  arch/x86/kvm/vmx.c | 34 ++++++++++++++++++++++------------
>  1 file changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6cf3972..8aefb91 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11259,6 +11259,24 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>         kvm_clear_interrupt_queue(vcpu);
>  }
>
> +static void load_vmcs12_mmu_host_state(struct kvm_vcpu *vcpu,
> +                       struct vmcs12 *vmcs12)
> +{
> +       u32 entry_failure_code;
> +
> +       nested_ept_uninit_mmu_context(vcpu);
> +
> +       /*
> +        * Only PDPTE load can fail as the value of cr3 was checked on entry and
> +        * couldn't have changed.
> +        */
> +       if (nested_vmx_load_cr3(vcpu, vmcs12->host_cr3, false, &entry_failure_code))
> +               nested_vmx_abort(vcpu, VMX_ABORT_LOAD_HOST_PDPTE_FAIL);
> +
> +       if (!enable_ept)
> +               vcpu->arch.walk_mmu->inject_page_fault = kvm_inject_page_fault;
> +}
> +
>  /*
>   * A part of what we need to when the nested L2 guest exits and we want to
>   * run its L1 parent, is to reset L1's guest state to the host state specified
> @@ -11272,7 +11290,6 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>                                    struct vmcs12 *vmcs12)
>  {
>         struct kvm_segment seg;
> -       u32 entry_failure_code;
>
>         if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_EFER)
>                 vcpu->arch.efer = vmcs12->host_ia32_efer;
> @@ -11299,17 +11316,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>         vcpu->arch.cr4_guest_owned_bits = ~vmcs_readl(CR4_GUEST_HOST_MASK);
>         vmx_set_cr4(vcpu, vmcs12->host_cr4);
>
> -       nested_ept_uninit_mmu_context(vcpu);
> -
> -       /*
> -        * Only PDPTE load can fail as the value of cr3 was checked on entry and
> -        * couldn't have changed.
> -        */
> -       if (nested_vmx_load_cr3(vcpu, vmcs12->host_cr3, false, &entry_failure_code))
> -               nested_vmx_abort(vcpu, VMX_ABORT_LOAD_HOST_PDPTE_FAIL);
> -
> -       if (!enable_ept)
> -               vcpu->arch.walk_mmu->inject_page_fault = kvm_inject_page_fault;
> +       load_vmcs12_mmu_host_state(vcpu, vmcs12);
>
>         if (enable_vpid) {
>                 /*
> @@ -11539,6 +11546,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>          * accordingly.
>          */
>         nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
> +
> +       load_vmcs12_mmu_host_state(vcpu, vmcs12);
> +
>         /*
>          * The emulated instruction was already skipped in
>          * nested_vmx_run, but the updated RIP was never
> --
> 2.7.4
>