linux-kernel - Re: [PATCH v3 64/75] x86/sev-es: Cache CPUID results for improved performance

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Date:   Fri, 12 Jun 2020 11:12:11 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     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>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 64/75] x86/sev-es: Cache CPUID results for improved
 performance

On Tue, Apr 28, 2020 at 05:17:14PM +0200, Joerg Roedel wrote:
> From: Mike Stunes <mstunes@...are.com>
> 
> To avoid a future VMEXIT for a subsequent CPUID function, cache the
> results returned by CPUID into an xarray.
> 
>  [tl: coding standard changes, register zero extension]
> 
> Signed-off-by: Mike Stunes <mstunes@...are.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> [ jroedel@...e.de: - Wrapped cache handling into vc_handle_cpuid_cached()
>                    - Used lower_32_bits() where applicable
> 		   - Moved cache_index out of struct es_em_ctxt ]
> Co-developed-by: Joerg Roedel <jroedel@...e.de>
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/kernel/sev-es-shared.c |  12 ++--
>  arch/x86/kernel/sev-es.c        | 119 +++++++++++++++++++++++++++++++-
>  2 files changed, 124 insertions(+), 7 deletions(-)

Okay, following the discussion, I am dropping this patch for now. We can
revisit CPUID caching later when we have a better justification.

Regards,

	Joerg