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References: <20211210154332.11526-1-brijesh.singh@amd.com> <20211210154332.11526-9-brijesh.singh@amd.com>
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In-Reply-To: <YbugbgXhApv9ECM2@dt>
From:   Mikolaj Lisik <lisik@google.com>
Date:   Thu, 16 Dec 2021 15:39:26 -0800
Message-ID: <CADtC8PX_bEk3rQR1sonbp-rX7rAG4fdbM41r3YLhfj3qWvqJrw@mail.gmail.com>
Subject: Re: [PATCH v8 08/40] x86/sev: Check the vmpl level
To:     Venu Busireddy <venu.busireddy@oracle.com>
Cc:     Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.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>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.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>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
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On Thu, Dec 16, 2021 at 12:24 PM Venu Busireddy
<venu.busireddy@oracle.com> wrote:
>
> On 2021-12-10 09:43:00 -0600, Brijesh Singh wrote:
> > Virtual Machine Privilege Level (VMPL) feature in the SEV-SNP architecture
> > allows a guest VM to divide its address space into four levels. The level
> > can be used to provide the hardware isolated abstraction layers with a VM.
> > The VMPL0 is the highest privilege, and VMPL3 is the least privilege.
> > Certain operations must be done by the VMPL0 software, such as:
> >
> > * Validate or invalidate memory range (PVALIDATE instruction)
> > * Allocate VMSA page (RMPADJUST instruction when VMSA=1)
> >
> > The initial SEV-SNP support requires that the guest kernel is running on
> > VMPL0. Add a check to make sure that kernel is running at VMPL0 before
> > continuing the boot. There is no easy method to query the current VMPL
> > level, so use the RMPADJUST instruction to determine whether the guest is
> > running at the VMPL0.
> >
> > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> > ---
> >  arch/x86/boot/compressed/sev.c    | 34 ++++++++++++++++++++++++++++---
> >  arch/x86/include/asm/sev-common.h |  1 +
> >  arch/x86/include/asm/sev.h        | 16 +++++++++++++++
> >  3 files changed, 48 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> > index a0708f359a46..9be369f72299 100644
> > --- a/arch/x86/boot/compressed/sev.c
> > +++ b/arch/x86/boot/compressed/sev.c
> > @@ -212,6 +212,31 @@ static inline u64 rd_sev_status_msr(void)
> >       return ((high << 32) | low);
> >  }
> >
> > +static void enforce_vmpl0(void)
> > +{
> > +     u64 attrs;
> > +     int err;
> > +
> > +     /*
> > +      * There is no straightforward way to query the current VMPL level. The
> > +      * simplest method is to use the RMPADJUST instruction to change a page
> > +      * permission to a VMPL level-1, and if the guest kernel is launched at
> > +      * a level <= 1, then RMPADJUST instruction will return an error.
>
> Perhaps a nit. When you say "level <= 1", do you mean a level lower than or
> equal to 1 semantically, or numerically?
>

+1 to this. Additionally I found the "level-1" confusing which I
interpreted as "level minus one".

Perhaps phrasing it as "level one", or "level=1" would be more explicit?