linux-kernel - Re: [PATCH 3/3] kernel: set USER_DS in kthread_use

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Date:   Thu, 16 Apr 2020 08:43:11 +0200
From:   Greg KH <greg@...ah.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Felipe Balbi <balbi@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-usb@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 3/3] kernel: set USER_DS in kthread_use_mm

On Thu, Apr 16, 2020 at 07:31:58AM +0200, Christoph Hellwig wrote:
> Some architectures like arm64 and s390 require USER_DS to be set for
> kernel threads to access user address space, which is the whole purpose
> of kthread_use_mm, but other like x86 don't.  That has lead to a huge
> mess where some callers are fixed up once they are tested on said
> architectures, while others linger around and yet other like io_uring
> try to do "clever" optimizations for what usually is just a trivial
> asignment to a member in the thread_struct for most architectures.
> 
> Make kthread_use_mm set USER_DS, and kthread_unuse_mm restore to the
> previous value instead.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> Acked-by: Michael S. Tsirkin <mst@...hat.com> [vhost]
> ---

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> [usb]