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    Subject[PATCH AUTOSEL 5.4 135/330] KVM: nVMX: Hold KVM's srcu lock when syncing vmcs12->shadow
    Date
    From: wanpeng li <wanpengli@tencent.com>

    [ Upstream commit c9dfd3fb08352d439f0399b6fabe697681d2638c ]

    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.

    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>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kvm/vmx/vmx.c | 11 +++++++++--
    1 file changed, 9 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
    index 3be65495aeb8a..a071eab3bab74 100644
    --- a/arch/x86/kvm/vmx/vmx.c
    +++ b/arch/x86/kvm/vmx/vmx.c
    @@ -1130,6 +1130,10 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
    vmx->guest_msrs[i].mask);

    }
    +
    + if (vmx->nested.need_vmcs12_to_shadow_sync)
    + nested_sync_vmcs12_to_shadow(vcpu);
    +
    if (vmx->guest_state_loaded)
    return;

    @@ -6485,8 +6489,11 @@ 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);
    + /*
    + * We did this in prepare_switch_to_guest, because it needs to
    + * be within srcu_read_lock.
    + */
    + WARN_ON_ONCE(vmx->nested.need_vmcs12_to_shadow_sync);

    if (test_bit(VCPU_REGS_RSP, (unsigned long *)&vcpu->arch.regs_dirty))
    vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]);
    --
    2.25.1
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