Re: [RFC PATCH v6 006/104] KVM: TDX: Detect CPU feature on kernel module initialization

[Sagi Shahar]

On Thu, May 5, 2022 at 11:15 AM <isaku.yamahata@xxxxxxxxx> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>
> TDX requires several initialization steps for KVM to create guest TDs.
> Detect CPU feature, enable VMX (TDX is based on VMX), detect TDX module
> availability, and initialize TDX module.  This patch implements the first
> step to detect CPU feature.  Because VMX isn't enabled yet by VMXON
> instruction on KVM kernel module initialization, defer further
> initialization step until VMX is enabled by hardware_enable callback.
>
> Introduce a module parameter, enable_tdx, to explicitly enable TDX KVM
> support.  It's off by default to keep same behavior for those who don't use
> TDX.  Implement CPU feature detection at KVM kernel module initialization
> as hardware_setup callback to check if CPU feature is available and get
> some CPU parameters.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  arch/x86/include/asm/tdx.h  |  2 ++
>  arch/x86/kvm/Makefile       |  1 +
>  arch/x86/kvm/vmx/main.c     | 18 ++++++++++++++++-
>  arch/x86/kvm/vmx/tdx.c      | 39 +++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/x86_ops.h  |  6 ++++++
>  arch/x86/virt/vmx/tdx/tdx.c |  3 ++-
>  6 files changed, 67 insertions(+), 2 deletions(-)
>  create mode 100644 arch/x86/kvm/vmx/tdx.c
>
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 513b9ce9a870..f8f459e28254 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -91,11 +91,13 @@ static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
>  #endif /* CONFIG_INTEL_TDX_GUEST && CONFIG_KVM_GUEST */
>
>  #ifdef CONFIG_INTEL_TDX_HOST
> +bool __seamrr_enabled(void);
>  void tdx_detect_cpu(struct cpuinfo_x86 *c);
>  int tdx_detect(void);
>  int tdx_init(void);
>  bool platform_has_tdx(void);
>  #else
> +static inline bool __seamrr_enabled(void) { return false; }
>  static inline void tdx_detect_cpu(struct cpuinfo_x86 *c) { }
>  static inline int tdx_detect(void) { return -ENODEV; }
>  static inline int tdx_init(void) { return -ENODEV; }
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index ee4d0999f20f..e2c05195cb95 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -24,6 +24,7 @@ kvm-$(CONFIG_KVM_XEN) += xen.o
>  kvm-intel-y            += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
>                            vmx/evmcs.o vmx/nested.o vmx/posted_intr.o vmx/main.o
>  kvm-intel-$(CONFIG_X86_SGX_KVM)        += vmx/sgx.o
> +kvm-intel-$(CONFIG_INTEL_TDX_HOST)     += vmx/tdx.o
>
>  kvm-amd-y              += svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o svm/sev.o
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 636768f5b985..fabf5f22c94f 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -6,6 +6,22 @@
>  #include "nested.h"
>  #include "pmu.h"
>
> +static bool __read_mostly enable_tdx = IS_ENABLED(CONFIG_INTEL_TDX_HOST);
> +module_param_named(tdx, enable_tdx, bool, 0444);
> +
> +static __init int vt_hardware_setup(void)
> +{
> +       int ret;
> +
> +       ret = vmx_hardware_setup();
> +       if (ret)
> +               return ret;
> +
> +       enable_tdx = enable_tdx && !tdx_hardware_setup(&vt_x86_ops);
> +
> +       return 0;
> +}
> +
>  struct kvm_x86_ops vt_x86_ops __initdata = {
>         .name = "kvm_intel",
>
> @@ -147,7 +163,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>  struct kvm_x86_init_ops vt_init_ops __initdata = {
>         .cpu_has_kvm_support = vmx_cpu_has_kvm_support,
>         .disabled_by_bios = vmx_disabled_by_bios,
> -       .hardware_setup = vmx_hardware_setup,
> +       .hardware_setup = vt_hardware_setup,
>         .handle_intel_pt_intr = NULL,
>
>         .runtime_ops = &vt_x86_ops,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> new file mode 100644
> index 000000000000..9e26e3fa60ee
> --- /dev/null
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -0,0 +1,39 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/cpu.h>
> +
> +#include <asm/tdx.h>
> +
> +#include "capabilities.h"
> +#include "x86_ops.h"
> +
> +#undef pr_fmt
> +#define pr_fmt(fmt) "tdx: " fmt
> +
> +static u64 hkid_mask __ro_after_init;
> +static u8 hkid_start_pos __ro_after_init;
> +
> +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> +{
> +       u32 max_pa;
> +
> +       if (!enable_ept) {
> +               pr_warn("Cannot enable TDX with EPT disabled\n");
> +               return -EINVAL;
> +       }
> +
> +       if (!platform_has_tdx()) {
> +               if (__seamrr_enabled())
> +                       pr_warn("Cannot enable TDX with SEAMRR disabled\n");

So if we fail for another reason (e.g. tdx_keyid_sufficient returns
false) we are going to fail silently and disable TDX without any log
saying what happened. This will make it difficult to debug TDX
initialization issues.

> +               return -ENODEV;
> +       }
> +
> +       if (WARN_ON_ONCE(x86_ops->tlb_remote_flush))
> +               return -EIO;
> +
> +       max_pa = cpuid_eax(0x80000008) & 0xff;
> +       hkid_start_pos = boot_cpu_data.x86_phys_bits;
> +       hkid_mask = GENMASK_ULL(max_pa - 1, hkid_start_pos);
> +       pr_info("hkid start pos %d mask 0x%llx\n", hkid_start_pos, hkid_mask);
> +
> +       return 0;
> +}
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 1d5dff7c0d96..7a885dc84183 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -122,4 +122,10 @@ void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu);
>  #endif
>  void vmx_setup_mce(struct kvm_vcpu *vcpu);
>
> +#ifdef CONFIG_INTEL_TDX_HOST
> +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
> +#else
> +static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return 0; }
> +#endif
> +
>  #endif /* __KVM_X86_VMX_X86_OPS_H */
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index b6c82e64ad54..e8044114079d 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -126,10 +126,11 @@ static int __init tdx_host_setup(char *s)
>  }
>  __setup("tdx_host=", tdx_host_setup);
>
> -static bool __seamrr_enabled(void)
> +bool __seamrr_enabled(void)
>  {
>         return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
>  }
> +EXPORT_SYMBOL_GPL(__seamrr_enabled);
>
>  static void detect_seam_bsp(struct cpuinfo_x86 *c)
>  {
> --
> 2.25.1
>

Sagi