Date:   Mon, 13 Dec 2021 16:54:53 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Maxim Levitsky <mlevitsk@redhat.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Lai Jiangshan <laijs@linux.alibaba.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Xiao Guangrong <guangrong.xiao@linux.intel.com>
Subject: Re: [PATCH 17/15] KVM: X86: Ensure pae_root to be reconstructed for
 shadow paging if the guest PDPTEs is changed
Message-ID: <Ybd63U3f9kXrMVEs@google.com>
References: <20211108124407.12187-1-jiangshanlai@gmail.com>
 <20211111144634.88972-1-jiangshanlai@gmail.com>
 <Ya/5MOYef4L4UUAb@google.com>
 <11219bdb-669c-cf6f-2a70-f4e5f909a2ad@redhat.com>
 <YbPBjdAz1GQGr8DT@google.com>
 <42701fedbe10acf164ec56818b941061be6ffd4e.camel@redhat.com>
 <56281d07-de85-69be-8855-71e7219e0227@redhat.com>
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On Sat, Dec 11, 2021, Paolo Bonzini wrote:
> On 12/11/21 07:56, Maxim Levitsky wrote:
> > > This apparently wasn't validated against a simple use case, let
> > > alone against things like migration with nested VMs, multliple L2s,
> > > etc...
> > 
> > I did validate the *SREGS2* against all the cases I could (like
> > migration, EPT/NPT disabled/etc. I even started testing SMM to see
> > how it affects PDPTRs, and patched seabios to use PAE paging. I still
> > could have missed something.
> 
> Don't worry, I think Sean was talking about patch 16 and specifically
> digging at me (who deserved it completely).

Yes, patch 16.  My goal wasn't to dig at anyone, I just wanted to dramatically
emphasize how ridiculousy fragile and complex the PDPTR crud is due to the number
of edge cases.