Date:   Thu, 16 Dec 2021 14:24:14 -0600
From:   Venu Busireddy <venu.busireddy@oracle.com>
To:     Brijesh Singh <brijesh.singh@amd.com>
Cc:     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>,
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        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
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        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v8 08/40] x86/sev: Check the vmpl level
Message-ID: <YbugbgXhApv9ECM2@dt>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-9-brijesh.singh@amd.com>
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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?

Venu