From:   Thomas Gleixner <tglx@linutronix.de>
To:     isaku.yamahata@intel.com, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, erdemaktas@google.com,
        Connor Kuehl <ckuehl@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Kai Huang <kai.huang@linux.intel.com>
Subject: Re: [RFC PATCH v3 18/59] KVM: x86: Add flag to mark TSC as
 immutable (for TDX)
In-Reply-To: <00772535f09b2bf98e6bc7008e81c6ffb381ed84.1637799475.git.isaku.yamahata@intel.com>
References: <cover.1637799475.git.isaku.yamahata@intel.com>
 <00772535f09b2bf98e6bc7008e81c6ffb381ed84.1637799475.git.isaku.yamahata@intel.com>
Date:   Thu, 25 Nov 2021 20:40:22 +0100
Message-ID: <87ilwgja6x.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Wed, Nov 24 2021 at 16:20, isaku yamahata wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> The TSC for TDX1 guests is fixed at TD creation time.  Add tsc_immutable

What's a TDX1 guest?

> to reflect that the TSC of the guest cannot be changed in any way, and
> use it to short circuit all paths that lead to one of the myriad TSC
> adjustment flows.

I can kinda see the reason for this being valuable on it's own, but in
general why does TDX need a gazillion flags to disable tons of different
things if _ALL_ these flags are going to be set by for TDX guests
anyway?

Seperate flags make only sense when they have a value on their own,
i.e. are useful for things outside of TDX. If not they are just useless
ballast.

Thanks,

        tglx