[PATCH V2 05/12] KVM: TDX: Implement TDX vcpu enter/exit path

Adrian Hunter
2025-01-29T10:00:04Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

Implement callbacks to enter/exit a TDX VCPU by calling tdh_vp_enter().
Ensure the TDX VCPU is in a correct state to run.

Do not pass arguments from/to vcpu->arch.regs[] unconditionally. Instead,
marshall state to/from the appropriate x86 registers only when needed,
i.e., to handle some TDVMCALL sub-leaves following KVM's ABI to leverage
the existing code.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
TD vcpu enter/exit v2:
- Move VCPU_TD_STATE_INITIALIZED check to tdx_vcpu_pre_run() (Xiaoyao)
- Check TD_STATE_RUNNABLE also in tdx_vcpu_pre_run() (Yan)
- Add back 'noinstr' for tdx_vcpu_enter_exit() (Sean)
- Add WARN_ON_ONCE if force_immediate_exit (Sean)
- Add vp_enter_args to vcpu_tdx to store the input/output arguments for
tdh_vp_enter().
- Don't copy arguments to/from vcpu->arch.regs[] unconditionally. (Sean)

TD vcpu enter/exit v1:
- Make argument of tdx_vcpu_enter_exit() struct kvm_vcpu.
- Update for the wrapper functions for SEAMCALLs. (Sean)
- Remove noinstr (Sean)
- Add a missing comma, clarify sched_in part, and update changelog to
match code by dropping the PMU related paragraph (Binbin)
https://lore.kernel.org/lkml/c0029d4d-3dee-4f11-a929-d64d2651bfb3@linux.intel.com/
- Remove the union tdx_exit_reason. (Sean)
https://lore.kernel.org/kvm/ZfSExlemFMKjBtZb@google.com/
- Remove the code of special handling of vcpu->kvm->vm_bugged (Rick)
https://lore.kernel.org/kvm/20240318234010.GD1645738@ls.amr.corp.intel.com/
- For !tdx->initialized case, set tdx->vp_enter_ret to TDX_SW_ERROR to avoid
collision with EXIT_REASON_EXCEPTION_NMI.

v19:
- Removed export_symbol_gpl(host_xcr0) to the patch that uses it

Changes v15 -> v16:
- use __seamcall_saved_ret()
- As struct tdx_module_args doesn't match with vcpu.arch.regs, copy regs
before/after calling __seamcall_saved_ret().
---
arch/x86/kvm/vmx/main.c | 20 ++++++++++++++--
arch/x86/kvm/vmx/tdx.c | 47 ++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/tdx.h | 3 +++
arch/x86/kvm/vmx/x86_ops.h | 7 ++++++
4 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 1cc1c06461f2..301c1a26606f 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -133,6 +133,22 @@ static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vmx_vcpu_load(vcpu, cpu);
}

+static int vt_vcpu_pre_run(struct kvm_vcpu *vcpu)
+{
+ if (is_td_vcpu(vcpu))
+ return tdx_vcpu_pre_run(vcpu);
+
+ return vmx_vcpu_pre_run(vcpu);
+}
+
+static fastpath_t vt_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
+{
+ if (is_td_vcpu(vcpu))
+ return tdx_vcpu_run(vcpu, force_immediate_exit);
+
+ return vmx_vcpu_run(vcpu, force_immediate_exit);
+}
+
static void vt_flush_tlb_all(struct kvm_vcpu *vcpu)
{
if (is_td_vcpu(vcpu)) {
@@ -272,8 +288,8 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.flush_tlb_gva = vt_flush_tlb_gva,
.flush_tlb_guest = vt_flush_tlb_guest,

- .vcpu_pre_run = vmx_vcpu_pre_run,
- .vcpu_run = vmx_vcpu_run,
+ .vcpu_pre_run = vt_vcpu_pre_run,
+ .vcpu_run = vt_vcpu_run,
.handle_exit = vmx_handle_exit,
.skip_emulated_instruction = vmx_skip_emulated_instruction,
.update_emulated_instruction = vmx_update_emulated_instruction,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index a7ebdafdfd82..95420ffd0022 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -11,6 +11,8 @@
#include "vmx.h"
#include "mmu/spte.h"
#include "common.h"
+#include <trace/events/kvm.h>
+#include "trace.h"

#pragma GCC poison to_vmx

@@ -673,6 +675,51 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
tdx->state = VCPU_TD_STATE_UNINITIALIZED;
}

+int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu)
+{
+ if (unlikely(to_tdx(vcpu)->state != VCPU_TD_STATE_INITIALIZED ||
+ to_kvm_tdx(vcpu->kvm)->state != TD_STATE_RUNNABLE))
+ return -EINVAL;
+
+ return 1;
+}
+
+static noinstr void tdx_vcpu_enter_exit(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+ guest_state_enter_irqoff();
+
+ tdx->vp_enter_ret = tdh_vp_enter(&tdx->vp, &tdx->vp_enter_args);
+
+ guest_state_exit_irqoff();
+}
+
+#define TDX_REGS_UNSUPPORTED_SET (BIT(VCPU_EXREG_RFLAGS) | \
+ BIT(VCPU_EXREG_SEGMENTS))
+
+fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
+{
+ /*
+ * force_immediate_exit requires vCPU entering for events injection with
+ * an immediately exit followed. But The TDX module doesn't guarantee
+ * entry, it's already possible for KVM to _think_ it completely entry
+ * to the guest without actually having done so.
+ * Since KVM never needs to force an immediate exit for TDX, and can't
+ * do direct injection, just warn on force_immediate_exit.
+ */
+ WARN_ON_ONCE(force_immediate_exit);
+
+ trace_kvm_entry(vcpu, force_immediate_exit);
+
+ tdx_vcpu_enter_exit(vcpu);
+
+ vcpu->arch.regs_avail &= ~TDX_REGS_UNSUPPORTED_SET;
+
+ trace_kvm_exit(vcpu, KVM_ISA_VMX);
+
+ return EXIT_FASTPATH_NONE;
+}

void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int pgd_level)
{
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index ba880dae547f..8339bbf0fdd4 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -46,11 +46,14 @@ enum vcpu_tdx_state {
struct vcpu_tdx {
struct kvm_vcpu vcpu;
struct vcpu_vt vt;
+ struct tdx_module_args vp_enter_args;

struct tdx_vp vp;

struct list_head cpu_list;

+ u64 vp_enter_ret;
+
enum vcpu_tdx_state state;
};

diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index ff6370787926..83aac44b779b 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -131,6 +131,8 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
int tdx_vcpu_create(struct kvm_vcpu *vcpu);
void tdx_vcpu_free(struct kvm_vcpu *vcpu);
void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
+int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu);
+fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit);

int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);

@@ -158,6 +160,11 @@ static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOP
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_load(struct kvm_vcpu *vcpu, int cpu) {}
+static inline int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
+static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
+{
+ return EXIT_FASTPATH_NONE;
+}

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

--
2.43.0