Re: [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret_msrs list

[Chao Gao <chao.gao@intel.com>]

On Wed, Dec 04, 2024 at 08:18:32AM +0200, Adrian Hunter wrote:
>On 4/12/24 03:25, Chao Gao wrote:
>>> +#define TDX_FEATURE_TSX (__feature_bit(X86_FEATURE_HLE) | __feature_bit(X86_FEATURE_RTM))
>>> +
>>> +static bool has_tsx(const struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	return entry->function == 7 && entry->index == 0 &&
>>> +	       (entry->ebx & TDX_FEATURE_TSX);
>>> +}
>>> +
>>> +static void clear_tsx(struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	entry->ebx &= ~TDX_FEATURE_TSX;
>>> +}
>>> +
>>> +static bool has_waitpkg(const struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	return entry->function == 7 && entry->index == 0 &&
>>> +	       (entry->ecx & __feature_bit(X86_FEATURE_WAITPKG));
>>> +}
>>> +
>>> +static void clear_waitpkg(struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	entry->ecx &= ~__feature_bit(X86_FEATURE_WAITPKG);
>>> +}
>>> +
>>> +static void tdx_clear_unsupported_cpuid(struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	if (has_tsx(entry))
>>> +		clear_tsx(entry);
>>> +
>>> +	if (has_waitpkg(entry))
>>> +		clear_waitpkg(entry);
>>> +}
>>> +
>>> +static bool tdx_unsupported_cpuid(const struct kvm_cpuid_entry2 *entry)
>>> +{
>>> +	return has_tsx(entry) || has_waitpkg(entry);
>>> +}
>> 
>> No need to check TSX/WAITPKG explicitly because setup_tdparams_cpuids() already
>> ensures that unconfigurable bits are not set by userspace.
>
>Aren't they configurable?

They are cleared from the configurable bitmap by tdx_clear_unsupported_cpuid(),
so they are not configurable from a userspace perspective. Did I miss anything?
KVM should check user inputs against its adjusted configurable bitmap, right?

>
>> 
>>> +
>>> #define KVM_TDX_CPUID_NO_SUBLEAF	((__u32)-1)
>>>
>>> static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char idx)
>>> @@ -124,6 +162,8 @@ static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char i
>>> 	/* Work around missing support on old TDX modules */
>>> 	if (entry->function == 0x80000008)
>>> 		entry->eax = tdx_set_guest_phys_addr_bits(entry->eax, 0xff);
>>> +
>>> +	tdx_clear_unsupported_cpuid(entry);
>>> }
>>>
>>> static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
>>> @@ -1235,6 +1275,9 @@ static int setup_tdparams_cpuids(struct kvm_cpuid2 *cpuid,
>>> 		if (!entry)
>>> 			continue;
>>>
>>> +		if (tdx_unsupported_cpuid(entry))
>>> +			return -EINVAL;
>>> +
>>> 		copy_cnt++;
>>>
>>> 		value = &td_params->cpuid_values[i];
>>> -- 
>>> 2.43.0
>>>
>