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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 7 Nov 2019 08:53:25 -0800
Message-ID: <CAHk-=wjtdCJYfy6nZSE7nKzUb1WLqh0B6MByTJCKe9OLOQ08PQ@mail.gmail.com>
Subject: Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Willy Tarreau <w@1wt.eu>, Peter Anvin <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Stephen Hemminger <stephen@networkplumber.org>,
        Juergen Gross <jgross@suse.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
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On Thu, Nov 7, 2019 at 8:45 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> Further a quick look shows that dosemu uses ioperm in a fine grained
> manner.  From memory it would allow a handful of ports to allow directly
> accessing a device and depended on the rest of the port accesses to be
> disallowed so it could trap and emulate them.

Yes. Making ioperm() some all-or-nothing thing would be horribly bad,
and has no real advantages that I can see.

               Linus