linux-kernel - Re: [PATCH v2] uaccess: add noop untagged

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Date:   Tue, 4 Jun 2019 09:28:41 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v2] uaccess: add noop untagged_addr definition

On Tue, Jun 04, 2019 at 02:04:47PM +0200, Andrey Konovalov wrote:
> Architectures that support memory tagging have a need to perform untagging
> (stripping the tag) in various parts of the kernel. This patch adds an
> untagged_addr() macro, which is defined as noop for architectures that do
> not support memory tagging. The oncoming patch series will define it at
> least for sparc64 and arm64.
> 
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
>  include/linux/mm.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0e8834ac32b7..dd0b5f4e1e45 100644
> +++ b/include/linux/mm.h
> @@ -99,6 +99,17 @@ extern int mmap_rnd_compat_bits __read_mostly;
>  #include <asm/pgtable.h>
>  #include <asm/processor.h>
>  
> +/*
> + * Architectures that support memory tagging (assigning tags to memory regions,
> + * embedding these tags into addresses that point to these memory regions, and
> + * checking that the memory and the pointer tags match on memory accesses)
> + * redefine this macro to strip tags from pointers.
> + * It's defined as noop for arcitectures that don't support memory tagging.
> + */
> +#ifndef untagged_addr
> +#define untagged_addr(addr) (addr)

Can you please make this a static inline instead of this macro? Then
we can actually know what the input/output types are supposed to be.

Is it

static inline unsigned long untagged_addr(void __user *ptr) {return ptr;}

?

Which would sort of make sense to me.

Jason