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

[Adrian Hunter <adrian.hunter@intel.com>]

On 4/12/24 08:37, Chao Gao wrote:
> 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?

Maybe I misunderstand but we rely on the TDX module to reject
invalid configuration.  We don't check exactly what is configurable
for the TDX Module.

TSX and WAITPKG are not invalid for the TDX Module, but KVM
must either support them by restoring their MSRs, or disallow
them.  This patch disallows them for now.

> 
>>
>>>
>>>> +
>>>> #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
>>>>
>>