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Date:   Mon, 6 Nov 2023 16:15:59 +0530
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Reply-To: nikunj@amd.com
Subject: Re: [PATCH v5 09/14] x86/sev: Add Secure TSC support for SNP guests
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org,
        bp@alien8.de, mingo@redhat.com, tglx@linutronix.de,
        dave.hansen@linux.intel.com, dionnaglaze@google.com,
        pgonda@google.com, seanjc@google.com, pbonzini@redhat.com
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From:   "Nikunj A. Dadhania" <nikunj@amd.com>
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On 11/2/2023 4:06 PM, Kirill A. Shutemov wrote:
> On Thu, Nov 02, 2023 at 11:11:52AM +0530, Nikunj A. Dadhania wrote:
>> On 10/31/2023 1:56 AM, Tom Lendacky wrote:
>>>> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
>>>> index cb0d6cd1c12f..e081ca4d5da2 100644
>>>> --- a/include/linux/cc_platform.h
>>>> +++ b/include/linux/cc_platform.h
>>>> @@ -90,6 +90,14 @@ enum cc_attr {
>>>>        * Examples include TDX Guest.
>>>>        */
>>>>       CC_ATTR_HOTPLUG_DISABLED,
>>>> +
>>>> +    /**
>>>> +     * @CC_ATTR_GUEST_SECURE_TSC: Secure TSC is active.
>>>> +     *
>>>> +     * The platform/OS is running as a guest/virtual machine and actively
>>>> +     * using AMD SEV-SNP Secure TSC feature.
>>>
>>> I think TDX also has a secure TSC like feature, so can this be generic?
>>
>> Yes, we can do that. In SNP case SecureTSC is an optional feature, not sure if that is the case for TDX as well.
>>
>> Kirill any inputs ?
> 
> We have several X86_FEATURE_ flags to indicate quality of TSC. Do we
> really need a CC_ATTR on top of that? Maybe SEV code could just set
> X86_FEATURE_ according to what its TSC can do?

For SEV-SNP, SEV_STATUS MSR has the information of various features
that have been enabled by the hypervisor. We will need a CC_ATTR for
these optional features.

Regards
Nikunj