linux-kernel - RE: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is active

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Date:   Tue, 25 Jul 2017 09:51:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Brijesh Singh' <brijesh.singh@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        "Paul Mackerras" <paulus@...ba.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Christoph Lameter" <cl@...ux.com>,
        Jonathan Corbet <corbet@....net>,
        Radim Krcmár <rkrcmar@...hat.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Airlie <airlied@...hat.com>, Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Laura Abbott <labbott@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric Biederman" <ebiederm@...ssion.com>,
        Tejun Heo <tj@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: RE: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV
 is active

From: Brijesh Singh
> Sent: 24 July 2017 20:08
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Secure Encrypted Virtualization (SEV) does not support string I/O, so
> unroll the string I/O operation into a loop operating on one element at
> a time.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/io.h | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index e080a39..2f3c002 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -327,14 +327,32 @@ static inline unsigned type in##bwl##_p(int port)			\
>  									\
>  static inline void outs##bwl(int port, const void *addr, unsigned long count) \
>  {

Is it even worth leaving these as inline functions?
Given the speed of IO cycles it is unlikely that the cost of calling a real
function will be significant.
The code bloat reduction will be significant.

	David