Cc:     brijesh.singh@amd.com, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@intel.com>,
        Peter Gonda <pgonda@google.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <Thomas.Lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>, tony.luck@intel.com,
        marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP)
 Hypervisor Support
To:     Sean Christopherson <seanjc@google.com>
References: <20210820155918.7518-1-brijesh.singh@amd.com>
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From:   Brijesh Singh <brijesh.singh@amd.com>
Message-ID: <f7b37ae0-4b7f-5b2a-1720-cfba0163de3e@amd.com>
Date:   Mon, 15 Nov 2021 12:58:54 -0600
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On 11/15/21 12:44 PM, Sean Christopherson wrote:
> On Mon, Nov 15, 2021, Brijesh Singh wrote:
>>
>> On 11/12/21 2:37 PM, Sean Christopherson wrote:
>>> This is the direction KVM TDX support is headed, though it's obviously still a WIP.
>>>
>>
>> Just curious, in this approach, how do you propose handling the host
>> kexec/kdump? If a kexec/kdump occurs while the VM is still active, the new
>> kernel will encounter the #PF (RMP violation) because some pages are still
>> marked 'private' in the RMP table.
> 
> There are two basic options: a) eagerly purge the RMP or b) lazily fixup the RMP
> on #PF.  Either approach can be made to work.  I'm not opposed to fixing up the RMP
> on #PF in the kexec/kdump case, I'm opposed to blindly updating the RMP on _all_
> RMP #PFs, i.e. the kernel should modify the RMP if and only if it knows that doing
> so is correct.  E.g. a naive lazy-fixup solution would be to track which pages have
> been sanitized and adjust the RMP on #PF to a page that hasn't yet been sanitized.
> 

Yap, I think option #a will require the current kernel to iterate 
through the entire memory and make it shared before booting the kexec 
kernel. It may bring another ask to track the guest private/shared on 
the host to minimize the iterations.

thanks