linux-kernel - Re: [PATCH v11 018/113] KVM: TDX: create/destroy VM structure

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Message-ID: <1c71eda35e03372f29162c6a5286f5b4d1e1d7e1.camel@intel.com>
Date:   Thu, 19 Jan 2023 23:55:10 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "zhi.wang.linux@...il.com" <zhi.wang.linux@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v11 018/113] KVM: TDX: create/destroy VM structure

On Thu, 2023-01-19 at 21:36 +0000, Sean Christopherson wrote:
> The least invasive idea I have is expand the TDP MMU's concept of "frozen" SPTEs
> and freeze (a.k.a. lock) the SPTE (KVM's mirror) until the corresponding S-EPT
> update completes.

This will introduce another "having-to-wait while SPTE is frozen" problem I
think, which IIUC means (one way is) you have to do some loop and retry, perhaps
similar to yield_safe.

> 
> The other idea is to scrap the mirror concept entirely, though I gotta imagine
> that would provide pretty awful performance.

Right.  I don't think this is a good option.