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;
Date:   Wed, 15 Jul 2020 11:34:26 +0200
From:   Joerg Roedel <jroedel@suse.de>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Joerg Roedel <joro@8bytes.org>, x86@kernel.org, hpa@zytor.com,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        David Rientjes <rientjes@google.com>,
        Cfir Cohen <cfir@google.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mike Stunes <mstunes@vmware.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Martin Radev <martin.b.radev@gmail.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v4 00/75] x86: SEV-ES Guest Support
Message-ID: <20200715093426.GK16200@suse.de>
References: <20200714120917.11253-1-joro@8bytes.org>
 <20200715092456.GE10769@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200715092456.GE10769@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jul 15, 2020 at 11:24:56AM +0200, Peter Zijlstra wrote:
> Can we get some more words -- preferably in actual code comments, on
> when exactly #VC happens?

Sure, will add this as a comment before the actual runtime VC handler.

> Because the only thing I remember is that #VC could happen on any memop,
> but I also have vague memories of that being a later extention.

Currently it is only raised when something happens that the hypervisor
intercepts, for example on a couple of instructions like CPUID,
RD/WRMSR, ..., or on MMIO/IOIO accesses.

With Secure Nested Paging (SNP), which needs additional enablement, a #VC can
happen on any memory access. I wrote the IST handling entry code for #VC
with that in mind, but do not actually enable it. This is the reason why
the #VC handler just panics the system when it ends up on the fall-back
(VC2) stack, with SNP enabled it needs to handle the SNP exit-codes in
that path.

Regards,

	Joerg