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From: Andrew Morton <akpm@linux-foundation.org>
To: Roman Penyaev <rpenyaev@suse.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
	Michal Hocko <mhocko@suse.com>,
	"David S . Miller" <davem@davemloft.net>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] mm/vmalloc: Make vmalloc_32_user() align base kernel virtual address to SHMLBA
Date: Tue, 8 Jan 2019 11:36:03 -0800	[thread overview]
Message-ID: <20190108113603.ea664e55869346bcb30c1433@linux-foundation.org> (raw)
In-Reply-To: <20190108110944.23591-1-rpenyaev@suse.de>

On Tue,  8 Jan 2019 12:09:44 +0100 Roman Penyaev <rpenyaev@suse.de> wrote:

> This patch repeats the original one from David S. Miller:
> 
>   2dca6999eed5 ("mm, perf_event: Make vmalloc_user() align base kernel virtual address to SHMLBA")
> 
> but for missed vmalloc_32_user() case, which also requires correct
> alignment of virtual address on kernel side to avoid D-caches
> aliases.  A bit of copy-paste from original patch to recover in
> memory of what is all about:
> 
>   When a vmalloc'd area is mmap'd into userspace, some kind of
>   co-ordination is necessary for this to work on platforms with cpu
>   D-caches which can have aliases.
> 
>   Otherwise kernel side writes won't be seen properly in userspace
>   and vice versa.
> 
>   If the kernel side mapping and the user side one have the same
>   alignment, modulo SHMLBA, this can work as long as VM_SHARED is
>   shared of VMA and for all current users this is true.  VM_SHARED
>   will force SHMLBA alignment of the user side mmap on platforms with
>   D-cache aliasing matters.

What are the user-visible runtime effects of this change?

Is a -stable backport needed?

  reply	other threads:[~2019-01-08 19:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-08 11:09 Roman Penyaev
2019-01-08 19:36 ` Andrew Morton [this message]
2019-01-09 10:08   ` Roman Penyaev

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