linux-kernel - Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler

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Date:   Tue, 14 Apr 2020 13:12:56 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime
 handler

On 4/14/20 1:04 PM, Tom Lendacky wrote:
>> set_memory_decrypted needs to check the return value. I see it
>> consistently return ENOMEM. I've traced that back to split_large_page
>> in arch/x86/mm/pat/set_memory.c.
> 
> At that point the guest won't be able to communicate with the
> hypervisor, too. Maybe we should BUG() here to terminate further
> processing?

Escalating an -ENOMEM into a crashed kernel seems a bit extreme.
Granted, the guest may be in an unrecoverable state, but the host
doesn't need to be too.