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    Subject[RFC PATCH v5 065/104] KVM: TDX: vcpu_run: save/restore host state(host kernel gs)
    Date
    From: Isaku Yamahata <isaku.yamahata@intel.com>

    On entering/exiting TDX vcpu, Preserved or clobbered CPU state is different
    from VMX case. Add TDX hooks to save/restore host/guest CPU state.
    Save/restore kernel GS base MSR.

    Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    ---
    arch/x86/kvm/vmx/main.c | 28 +++++++++++++++++++++++++--
    arch/x86/kvm/vmx/tdx.c | 39 ++++++++++++++++++++++++++++++++++++++
    arch/x86/kvm/vmx/tdx.h | 4 ++++
    arch/x86/kvm/vmx/x86_ops.h | 4 ++++
    4 files changed, 73 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
    index 2e5a7a72d560..f9d43f2de145 100644
    --- a/arch/x86/kvm/vmx/main.c
    +++ b/arch/x86/kvm/vmx/main.c
    @@ -89,6 +89,30 @@ static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
    return vmx_vcpu_reset(vcpu, init_event);
    }

    +static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
    +{
    + /*
    + * All host state is saved/restored across SEAMCALL/SEAMRET, and the
    + * guest state of a TD is obviously off limits. Deferring MSRs and DRs
    + * is pointless because the TDX module needs to load *something* so as
    + * not to expose guest state.
    + */
    + if (is_td_vcpu(vcpu)) {
    + tdx_prepare_switch_to_guest(vcpu);
    + return;
    + }
    +
    + vmx_prepare_switch_to_guest(vcpu);
    +}
    +
    +static void vt_vcpu_put(struct kvm_vcpu *vcpu)
    +{
    + if (is_td_vcpu(vcpu))
    + return tdx_vcpu_put(vcpu);
    +
    + return vmx_vcpu_put(vcpu);
    +}
    +
    static fastpath_t vt_vcpu_run(struct kvm_vcpu *vcpu)
    {
    if (is_td_vcpu(vcpu))
    @@ -174,9 +198,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
    .vcpu_free = vt_vcpu_free,
    .vcpu_reset = vt_vcpu_reset,

    - .prepare_guest_switch = vmx_prepare_switch_to_guest,
    + .prepare_guest_switch = vt_prepare_switch_to_guest,
    .vcpu_load = vmx_vcpu_load,
    - .vcpu_put = vmx_vcpu_put,
    + .vcpu_put = vt_vcpu_put,

    .update_exception_bitmap = vmx_update_exception_bitmap,
    .get_msr_feature = vmx_get_msr_feature,
    diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
    index ebe4f9bf19e7..7a288aae03ba 100644
    --- a/arch/x86/kvm/vmx/tdx.c
    +++ b/arch/x86/kvm/vmx/tdx.c
    @@ -1,5 +1,6 @@
    // SPDX-License-Identifier: GPL-2.0
    #include <linux/cpu.h>
    +#include <linux/mmu_context.h>

    #include <asm/tdx.h>

    @@ -407,6 +408,9 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
    vcpu->arch.guest_state_protected =
    !(to_kvm_tdx(vcpu->kvm)->attributes & TDX_TD_ATTRIBUTE_DEBUG);

    + tdx->host_state_need_save = true;
    + tdx->host_state_need_restore = false;
    +
    return 0;

    free_tdvpx:
    @@ -420,6 +424,39 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
    return ret;
    }

    +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
    +{
    + struct vcpu_tdx *tdx = to_tdx(vcpu);
    +
    + if (!tdx->host_state_need_save)
    + return;
    +
    + if (likely(is_64bit_mm(current->mm)))
    + tdx->msr_host_kernel_gs_base = current->thread.gsbase;
    + else
    + tdx->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
    +
    + tdx->host_state_need_save = false;
    +}
    +
    +static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
    +{
    + struct vcpu_tdx *tdx = to_tdx(vcpu);
    +
    + tdx->host_state_need_save = true;
    + if (!tdx->host_state_need_restore)
    + return;
    +
    + wrmsrl(MSR_KERNEL_GS_BASE, tdx->msr_host_kernel_gs_base);
    + tdx->host_state_need_restore = false;
    +}
    +
    +void tdx_vcpu_put(struct kvm_vcpu *vcpu)
    +{
    + vmx_vcpu_pi_put(vcpu);
    + tdx_prepare_switch_to_host(vcpu);
    +}
    +
    void tdx_vcpu_free(struct kvm_vcpu *vcpu)
    {
    struct vcpu_tdx *tdx = to_tdx(vcpu);
    @@ -535,6 +572,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)

    tdx_vcpu_enter_exit(vcpu, tdx);

    + tdx->host_state_need_restore = true;
    +
    vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
    trace_kvm_exit(vcpu, KVM_ISA_VMX);

    diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
    index e950404ce5de..8b1cf9c158e3 100644
    --- a/arch/x86/kvm/vmx/tdx.h
    +++ b/arch/x86/kvm/vmx/tdx.h
    @@ -84,6 +84,10 @@ struct vcpu_tdx {
    union tdx_exit_reason exit_reason;

    bool initialized;
    +
    + bool host_state_need_save;
    + bool host_state_need_restore;
    + u64 msr_host_kernel_gs_base;
    };

    static inline bool is_td(struct kvm *kvm)
    diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
    index 44404dd25737..8b871c5f52cf 100644
    --- a/arch/x86/kvm/vmx/x86_ops.h
    +++ b/arch/x86/kvm/vmx/x86_ops.h
    @@ -141,6 +141,8 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu);
    void tdx_vcpu_free(struct kvm_vcpu *vcpu);
    void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
    fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu);
    +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
    +void tdx_vcpu_put(struct kvm_vcpu *vcpu);

    int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
    int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
    @@ -162,6 +164,8 @@ static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
    static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
    static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
    static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { return EXIT_FASTPATH_NONE; }
    +static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
    +static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}

    static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
    static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
    --
    2.25.1
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