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

Borislav Petkov
2017-07-26T04:28:40Z

On Mon, Jul 24, 2017 at 02:07:43PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
>
> 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-5C7GfCeVMHo@public.gmane.org>
> Signed-off-by: Brijesh Singh <brijesh.singh-5C7GfCeVMHo@public.gmane.org>
> ---
> 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)
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