Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <8ba6676471dc8c8219e35d6a1695febaea20bb0b.camel@redhat.com>
Subject: Re: [PATCH 3/3] KVM: SVM: allow to intercept all exceptions for
 debug
From:   Maxim Levitsky <mlevitsk@redhat.com>
To:     Joerg Roedel <joro@8bytes.org>
Cc:     kvm@vger.kernel.org, Vitaly Kuznetsov <vkuznets@redhat.com>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpengli@tencent.com>,
        Kieran Bingham <kbingham@kernel.org>,
        Jessica Yu <jeyu@kernel.org>,
        Jan Kiszka <jan.kiszka@siemens.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Jim Mattson <jmattson@google.com>,
        Borislav Petkov <bp@alien8.de>,
        Stefano Garzarella <sgarzare@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>
Date:   Thu, 18 Mar 2021 11:24:25 +0200
In-Reply-To: <YFMbLWLlGgbOJuN/@8bytes.org>
References: <20210315221020.661693-1-mlevitsk@redhat.com>
         <20210315221020.661693-4-mlevitsk@redhat.com> <YFBtI55sVzIJ15U+@8bytes.org>
         <4116d6ce75a85faccfe7a2b3967528f0561974ae.camel@redhat.com>
         <YFMbLWLlGgbOJuN/@8bytes.org>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Thu, 2021-03-18 at 10:19 +0100, Joerg Roedel wrote:
> On Tue, Mar 16, 2021 at 12:51:20PM +0200, Maxim Levitsky wrote:
> > I agree but what is wrong with that? 
> > This is a debug feature, and it only can be enabled by the root,
> > and so someone might actually want this case to happen
> > (e.g to see if a SEV guest can cope with extra #VC exceptions).
> 
> That doesn't make sense, we know that and SEV-ES guest can't cope with
> extra #VC exceptions, so there is no point in testing this. It is more a
> way to shot oneself into the foot for the user and a potential source of
> bug reports for SEV-ES guests.

But again this is a debug feature, and it is intended to allow the user
to shoot himself in the foot. Bug reports for a debug feature
are autoclosed. It is no different from say poking kernel memory with
its built-in gdbstub, for example.

Best regards,
	Maxim Levitsky

> 
> 
> > I have nothing against not allowing this for SEV-ES guests though.
> > What do you think?
> 
> I think SEV-ES guests should only have the intercept bits set which
> guests acutally support

> 
> Regards,
> 
> 	Joerg
>