[PATCH v2 14/24] KVM: TDX: Require TDP MMU and mmio caching for TDX

Yan Zhao
2024-11-12T07:39:51Z

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

Disable TDX support when TDP MMU or mmio caching aren't supported.

As TDP MMU is becoming main stream than the legacy MMU, the legacy MMU
support for TDX isn't implemented.

TDX requires KVM mmio caching. Without mmio caching, KVM will go to MMIO
emulation without installing SPTEs for MMIOs. However, TDX guest is
protected and KVM would meet errors when trying to emulate MMIOs for TDX
guest during instruction decoding. So, TDX guest relies on SPTEs being
installed for MMIOs, which are with no RWX bits and with VE suppress bit
unset, to inject VE to TDX guest. The TDX guest would then issue TDVMCALL
in the VE handler to perform instruction decoding and have host do MMIO
emulation.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Co-developed-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
TDX MMU part 2 v2:
- Added Paolo's rb.

TDX MMU part 2 v1:
- Addressed Binbin's comment by massaging Isaku's updated comments and
adding more explanations about instroducing mmio caching.
- Addressed Sean's comments of v19 according to Isaku's update but
kept the warning for MOVDIR64B.
- Move code change in tdx_hardware_setup() to __tdx_bringup() since the
former has been removed.
---
arch/x86/kvm/mmu/mmu.c | 1 +
arch/x86/kvm/vmx/main.c | 1 +
arch/x86/kvm/vmx/tdx.c | 8 +++-----
3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3a338df541c1..e2f75c8145fd 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -110,6 +110,7 @@ static bool __ro_after_init tdp_mmu_allowed;
#ifdef CONFIG_X86_64
bool __read_mostly tdp_mmu_enabled = true;
module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0444);
+EXPORT_SYMBOL_GPL(tdp_mmu_enabled);
#endif

static int max_huge_page_level __read_mostly;
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 3c292b4a063a..a34c0bebe1c3 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -3,6 +3,7 @@

#include "x86_ops.h"
#include "vmx.h"
+#include "mmu.h"
#include "nested.h"
#include "pmu.h"
#include "posted_intr.h"
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 38369cafc175..8832f76e4a22 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1412,16 +1412,14 @@ static int __init __tdx_bringup(void)
const struct tdx_sys_info_td_conf *td_conf;
int r;

+ if (!tdp_mmu_enabled || !enable_mmio_caching)
+ return -EOPNOTSUPP;
+
if (!cpu_feature_enabled(X86_FEATURE_MOVDIR64B)) {
pr_warn("MOVDIR64B is reqiured for TDX\n");
return -EOPNOTSUPP;
}

- if (!enable_ept) {
- pr_err("Cannot enable TDX with EPT disabled.\n");
- return -EINVAL;
- }
-
/*
* Enabling TDX requires enabling hardware virtualization first,
* as making SEAMCALLs requires CPU being in post-VMXON state.
--
2.43.2