linux-kernel - Re: [RFC Part1 PATCH v3 03/17] x86/mm: Secure Encrypted Virtualization (SEV) support

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Date:   Wed, 26 Jul 2017 06:28:40 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC Part1 PATCH v3 03/17] x86/mm: Secure Encrypted
 Virtualization (SEV) support

On Mon, Jul 24, 2017 at 02:07:43PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Provide support for Secure Encyrpted Virtualization (SEV). This initial

Your subject misses a verb and patch subjects should have an active verb
denoting what the patch does. The sentence above is a good example.

> support defines a flag that is used by the kernel to determine if it is
> running with SEV active.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/mem_encrypt.h | 2 ++
>  arch/x86/mm/mem_encrypt.c          | 3 +++
>  include/linux/mem_encrypt.h        | 8 +++++++-
>  3 files changed, 12 insertions(+), 1 deletion(-)

...

> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 0fbd092..1e4643e 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -40,6 +40,9 @@ static char sme_cmdline_off[] __initdata = "off";
>  unsigned long sme_me_mask __section(.data) = 0;
>  EXPORT_SYMBOL_GPL(sme_me_mask);
>  
> +unsigned int sev_enabled __section(.data) = 0;
> +EXPORT_SYMBOL_GPL(sev_enabled);

So sev_enabled is a pure bool used only in bool context, not like
sme_me_mask whose value is read too. Which means, you can make the
former static and query it only through accessor functions.

>  /* Buffer used for early in-place encryption by BSP, no locking needed */
>  static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);
>  
> diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
> index 1255f09..ea0831a 100644
> --- a/include/linux/mem_encrypt.h
> +++ b/include/linux/mem_encrypt.h
> @@ -22,12 +22,18 @@
>  #else	/* !CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
>  #define sme_me_mask	0UL
> +#define sev_enabled	0
>  
>  #endif	/* CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
>  static inline bool sme_active(void)
>  {
> -	return !!sme_me_mask;
> +	return (sme_me_mask && !sev_enabled);

You don't need the brackets. Below too.

> +}
> +
> +static inline bool sev_active(void)
> +{
> +	return (sme_me_mask && sev_enabled);
>  }

So this is confusing, TBH. SME and SEV are not mutually exclusive and
yet the logic here says so. Why?

I mean, in the hypervisor context, sme_active() is still true.

/me is confused.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--