linux-kernel - Re: [PATCH v2 6/9] userfaultfd/selftests: create alias mappings in the shmem test

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Message-ID: <20210413201750.GF4440@xz-x1>
Date:   Tue, 13 Apr 2021 16:17:50 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Joe Perches <joe@...ches.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Shaohua Li <shli@...com>, Shuah Khan <shuah@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Wang Qing <wangqing@...o.com>, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        Brian Geffon <bgeffon@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v2 6/9] userfaultfd/selftests: create alias mappings in
 the shmem test

On Mon, Apr 12, 2021 at 10:17:18PM -0700, Axel Rasmussen wrote:
>  static void shmem_allocate_area(void **alloc_area)
>  {
> -	unsigned long offset =
> -		alloc_area == (void **)&area_src ? 0 : nr_pages * page_size;
> +	void *area_alias = NULL;
> +	bool is_src = alloc_area == (void **)&area_src;
> +	unsigned long offset = is_src ? 0 : nr_pages * page_size;
>  
>  	*alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
>  			   MAP_SHARED, shm_fd, offset);
>  	if (*alloc_area == MAP_FAILED)
>  		err("mmap of memfd failed");
> +
> +	area_alias = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
> +			  MAP_SHARED, shm_fd, offset);
> +	if (area_alias == MAP_FAILED)
> +		err("mmap of memfd alias failed");
> +
> +	if (is_src)
> +		area_src_alias = area_alias;
> +	else
> +		area_dst_alias = area_alias;
> +}

It would be nice if shmem_allocate_area() could merge with
hugetlb_allocate_area() somehow, but not that urgent.

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

-- 
Peter Xu