linux-kernel - Re: [PATCH v14 09/10] arch, mm: wire up memfd

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Message-Id: <20201203153916.91f0f80dcb8a0fa81fc341fa@linux-foundation.org>
Date:   Thu, 3 Dec 2020 15:39:16 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v14 09/10] arch, mm: wire up memfd_secret system call
 were relevant

On Thu,  3 Dec 2020 08:29:48 +0200 Mike Rapoport <rppt@...nel.org> wrote:

> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> Wire up memfd_secret system call on architectures that define
> ARCH_HAS_SET_DIRECT_MAP, namely arm64, risc-v and x86.
> 
> ...
>
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -861,9 +861,13 @@ __SYSCALL(__NR_faccessat2, sys_faccessat2)
>  __SYSCALL(__NR_process_madvise, sys_process_madvise)
>  #define __NR_watch_mount 441
>  __SYSCALL(__NR_watch_mount, sys_watch_mount)
> +#ifdef __ARCH_WANT_MEMFD_SECRET
> +#define __NR_memfd_secret 442
> +__SYSCALL(__NR_memfd_secret, sys_memfd_secret)
> +#endif

Why do we add the ifdef?  Can't we simply define the syscall on all
architectures and let sys_ni do its thing?