Date:   Mon, 15 Nov 2021 15:33:03 +0000
From:   "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To:     Joerg Roedel <jroedel@suse.de>
Cc:     Sean Christopherson <seanjc@google.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@intel.com>,
        Peter Gonda <pgonda@google.com>,
        Brijesh Singh <brijesh.singh@amd.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>,
        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
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References: <20210820155918.7518-1-brijesh.singh@amd.com>
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* Joerg Roedel (jroedel@suse.de) wrote:
> On Mon, Nov 15, 2021 at 12:30:59PM +0000, Dr. David Alan Gilbert wrote:
> > Still; I wonder if it's best to kill the guest - maybe it's best for
> > the host to kill the guest and leave behind diagnostics of what
> > happened; for someone debugging the crash, it's going to be less useful
> > to know that page X was wrongly accessed (which is what the guest would
> > see), and more useful to know that it was the kernel's vhost-... driver
> > that accessed it.
> 
> I is best to let the guest #VC on the page when this happens. If it
> happened because of a guest bug all necessary debugging data is in the
> guest and only the guest owner can obtain it.
> 
> Then the guest owner can do a kdump on this unexpected #VC and collect
> the data to debug the issue. With just killing the guest from the host
> side this data would be lost.

How would you debug an unexpected access by the host kernel using a
guests kdump?

Dave

> Regards,
> 
> 	Joerg
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK