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SubjectRe: [PATCH v2] KVM: X86: Grab KVM's srcu lock when accessing hv assist page
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On 14/02/20 10:16, Wanpeng Li wrote:
> From: wanpeng li <wanpengli@tencent.com>
>
> For the duration of mapping eVMCS, it derefences ->memslots without holding
> ->srcu or ->slots_lock when accessing hv assist page. This patch fixes it by
> moving nested_sync_vmcs12_to_shadow to prepare_guest_switch, where the SRCU
> is already taken.

Looks good, but I'd like an extra review from Sean or Vitaly.

We also should add a WARN_ON_ONCE that replaces the previous location of
the "if (vmx->nested.need_vmcs12_to_shadow_sync)", but I can do that myself.

Thanks,

Paolo

> It can be reproduced by running kvm's evmcs_test selftest.
>
> =============================
> warning: suspicious rcu usage
> 5.6.0-rc1+ #53 tainted: g w ioe
> -----------------------------
> ./include/linux/kvm_host.h:623 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by evmcs_test/8507:
> #0: ffff9ddd156d00d0 (&vcpu->mutex){+.+.}, at:
> kvm_vcpu_ioctl+0x85/0x680 [kvm]
>
> stack backtrace:
> cpu: 6 pid: 8507 comm: evmcs_test tainted: g w ioe 5.6.0-rc1+ #53
> hardware name: dell inc. optiplex 7040/0jctf8, bios 1.4.9 09/12/2016
> call trace:
> dump_stack+0x68/0x9b
> kvm_read_guest_cached+0x11d/0x150 [kvm]
> kvm_hv_get_assist_page+0x33/0x40 [kvm]
> nested_enlightened_vmentry+0x2c/0x60 [kvm_intel]
> nested_vmx_handle_enlightened_vmptrld.part.52+0x32/0x1c0 [kvm_intel]
> nested_sync_vmcs12_to_shadow+0x439/0x680 [kvm_intel]
> vmx_vcpu_run+0x67a/0xe60 [kvm_intel]
> vcpu_enter_guest+0x35e/0x1bc0 [kvm]
> kvm_arch_vcpu_ioctl_run+0x40b/0x670 [kvm]
> kvm_vcpu_ioctl+0x370/0x680 [kvm]
> ksys_ioctl+0x235/0x850
> __x64_sys_ioctl+0x16/0x20
> do_syscall_64+0x77/0x780
> entry_syscall_64_after_hwframe+0x49/0xbe
>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9a66648..6bd6ca4 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1214,6 +1214,9 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>
> vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base);
> vmx->guest_state_loaded = true;
> +
> + if (vmx->nested.need_vmcs12_to_shadow_sync)
> + nested_sync_vmcs12_to_shadow(vcpu);
> }
>
> static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
> @@ -6480,9 +6483,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> vmcs_write32(PLE_WINDOW, vmx->ple_window);
> }
>
> - if (vmx->nested.need_vmcs12_to_shadow_sync)
> - nested_sync_vmcs12_to_shadow(vcpu);
> -
> if (kvm_register_is_dirty(vcpu, VCPU_REGS_RSP))
> vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]);
> if (kvm_register_is_dirty(vcpu, VCPU_REGS_RIP))
> --
> 2.7.4
>

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