Re: [PATCH 10/21] KVM: TDX: Require TDP MMU and mmio caching for TDX

[Paolo Bonzini]

On 9/4/24 05:07, Rick Edgecombe wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> Co-developed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
> 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 01808cdf8627..d26b235d8f84 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 c9dfa3aa866c..2cc29d0fc279 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 25c24901061b..0c08062ef99f 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1474,16 +1474,14 @@ 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.

Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>