linux-kernel - Re: [PATCH v7 1/6] userfaultfd: add minor fault registration mode

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Message-ID: <20210223152015.GA154711@xz-x1>
Date:   Tue, 23 Feb 2021 10:20:15 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Huang Ying <ying.huang@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Koutný <mkoutny@...e.com>,
        Michel Lespinasse <walken@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>, Shaohua Li <shli@...com>,
        Shawn Anastasio <shawn@...stas.io>,
        Steven Rostedt <rostedt@...dmis.org>,
        Steven Price <steven.price@....com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Adam Ruprecht <ruprecht@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v7 1/6] userfaultfd: add minor fault registration mode

On Thu, Feb 18, 2021 at 04:48:19PM -0800, Axel Rasmussen wrote:

[...]

> @@ -1290,14 +1299,20 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
>  	ret = -EINVAL;
>  	if (!uffdio_register.mode)
>  		goto out;
> -	if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
> -				     UFFDIO_REGISTER_MODE_WP))
> +	if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
>  		goto out;
>  	vm_flags = 0;
>  	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
>  		vm_flags |= VM_UFFD_MISSING;
>  	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
>  		vm_flags |= VM_UFFD_WP;
> +	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
> +		/* VM_UFFD_MINOR == VM_NONE if this arch doesn't support it. */

How about check CONFIG_HAVE_ARCH_USERFAULTFD_MINOR below directly instead of
commenting?

> +		ret = -EINVAL;

Should be able to drop this line too since ret is -EINVAL already?

> +		if (!VM_UFFD_MINOR)
> +			goto out;
> +		vm_flags |= VM_UFFD_MINOR;
> +	}

[...]

> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index 67018d367b9f..a743a0f9ebde 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -137,6 +137,12 @@ IF_HAVE_PG_ARCH_2(PG_arch_2,		"arch_2"	)
>  #define IF_HAVE_VM_SOFTDIRTY(flag,name)
>  #endif
>  
> +#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> +# define IF_HAVE_UFFD_MINOR(flag, name) {flag, name},
> +#else
> +# define IF_HAVE_UFFD_MINOR(flag, name)
> +#endif
> +
>  #define __def_vmaflag_names						\
>  	{VM_READ,			"read"		},		\
>  	{VM_WRITE,			"write"		},		\
> @@ -148,6 +154,7 @@ IF_HAVE_PG_ARCH_2(PG_arch_2,		"arch_2"	)
>  	{VM_MAYSHARE,			"mayshare"	},		\
>  	{VM_GROWSDOWN,			"growsdown"	},		\
>  	{VM_UFFD_MISSING,		"uffd_missing"	},		\
> +IF_HAVE_UFFD_MINOR(VM_UFFD_MINOR,	"uffd_minor"	)		\
>  	{VM_PFNMAP,			"pfnmap"	},		\
>  	{VM_DENYWRITE,			"denywrite"	},		\
>  	{VM_UFFD_WP,			"uffd_wp"	},		\
> @@ -169,7 +176,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
>  	{VM_MIXEDMAP,			"mixedmap"	},		\
>  	{VM_HUGEPAGE,			"hugepage"	},		\
>  	{VM_NOHUGEPAGE,			"nohugepage"	},		\
> -	{VM_MERGEABLE,			"mergeable"	}		\
> +	{VM_MERGEABLE,			"mergeable"	}

This change seems irrelevant.

If you agree with above comments, please feel free to add:

Reviewed-by: Peter Xu <peterx@...hat.com>

Thanks,

-- 
Peter Xu