Re: [PATCH 22/25] KVM: TDX: Use guest physical address to configure EPT level and GPAW

[Xiaoyao Li]

On 8/13/2024 6:48 AM, Rick Edgecombe wrote:
> From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
>
> KVM reports guest physical address in CPUID.0x800000008.EAX[23:16],
> which is similar to TDX's GPAW. Use this field as the interface for
> userspace to configure the GPAW and EPT level for TDs.
>
> Note,
>
> 1. only value 48 and 52 are supported. 52 means GPAW-52 and EPT level
>     5, and 48 means GPAW-48 and EPT level 4.
> 2. value 48, i.e., GPAW-48 is always supported. value 52 is only
>     supported when the platform supports 5 level EPT.
>
> Current TDX module doesn't support max_gpa configuration. However
> current implementation relies on max_gpa to configure  EPT level and
> GPAW. Hack KVM to make it work.

This patch needs to be squashed into patch 14.

> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
> uAPI breakout v1:
>   - New patch
> ---
>   arch/x86/kvm/vmx/tdx.c | 32 +++++++++++++++++++-------------
>   1 file changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index fe2bbc2ced41..c6bfeb0b3cc9 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -514,23 +514,22 @@ static int setup_tdparams_eptp_controls(struct kvm_cpuid2 *cpuid,
>   					struct td_params *td_params)
>   {
>   	const struct kvm_cpuid_entry2 *entry;
> -	int max_pa = 36;
> +	int guest_pa;
>   
>   	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0x80000008, 0);
> -	if (entry)
> -		max_pa = entry->eax & 0xff;
> +	if (!entry)
> +		return -EINVAL;
> +
> +	guest_pa = (entry->eax >> 16) & 0xff;
> +
> +	if (guest_pa != 48 && guest_pa != 52)
> +		return -EINVAL;
> +
> +	if (guest_pa == 52 && !cpu_has_vmx_ept_5levels())
> +		return -EINVAL;
>   
>   	td_params->eptp_controls = VMX_EPTP_MT_WB;
> -	/*
> -	 * No CPU supports 4-level && max_pa > 48.
> -	 * "5-level paging and 5-level EPT" section 4.1 4-level EPT
> -	 * "4-level EPT is limited to translating 48-bit guest-physical
> -	 *  addresses."
> -	 * cpu_has_vmx_ept_5levels() check is just in case.
> -	 */
> -	if (!cpu_has_vmx_ept_5levels() && max_pa > 48)
> -		return -EINVAL;
> -	if (cpu_has_vmx_ept_5levels() && max_pa > 48) {
> +	if (guest_pa == 52) {
>   		td_params->eptp_controls |= VMX_EPTP_PWL_5;
>   		td_params->exec_controls |= TDX_EXEC_CONTROL_MAX_GPAW;
>   	} else {
> @@ -576,6 +575,9 @@ static int setup_tdparams_cpuids(struct kvm_cpuid2 *cpuid,
>   		value->ebx = entry->ebx;
>   		value->ecx = entry->ecx;
>   		value->edx = entry->edx;
> +
> +		if (c->leaf == 0x80000008)
> +			value->eax &= 0xff00ffff;
>   	}
>   
>   	return 0;
> @@ -1277,6 +1279,10 @@ static int __init setup_kvm_tdx_caps(void)
>   		memcpy(dest, &source, sizeof(struct kvm_tdx_cpuid_config));
>   		if (dest->sub_leaf == KVM_TDX_CPUID_NO_SUBLEAF)
>   			dest->sub_leaf = 0;
> +
> +		/* Work around missing support on old TDX modules */
> +		if (dest->leaf == 0x80000008)
> +			dest->eax |= 0x00ff0000;
>   	}
>   
>   	return 0;