On 4/12/24 13:13, Chao Gao wrote:
> On Wed, Dec 04, 2024 at 08:57:23AM +0200, Adrian Hunter wrote:
>> 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.
>
> Ok, this is what I missed. I thought KVM validated user input and masked
> out all unsupported features. sorry for this.
>
>>
>> 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.
>
> Yes. I agree. what if a new feature (supported by a future TDX module) also
> needs KVM to restore some MSRs? current KVM will allow it to be exposed (since
> only TSX/WAITPKG are checked); then some MSRs may get corrupted. I may think
> this is not a good design. Current KVM should work with future TDX modules.
With respect to CPUID, I gather this kind of thing has been
discussed, such as here:
https://lore.kernel.org/all/ZhVsHVqaff7AKagu@xxxxxxxxxx/
and Rick and Xiaoyao are working on something.
In general, I would expect a new TDX Module would advertise support for
new features, but KVM would have to opt in to use them.
