linux-kernel - Re: [PATCH v2] x86/vm86/32: Remove VM86_SCREEN

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Message-ID: <65ca981d-1a23-d8fe-71fb-efe17befe8df@yandex.ru>
Date:   Tue, 19 Jan 2021 22:13:01 +0300
From:   stsp <stsp2@...dex.ru>
To:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linux-MM <linux-mm@...ck.org>, Jason Gunthorpe <jgg@...pe.ca>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jann Horn <jannh@...gle.com>, Jan Kara <jack@...e.cz>,
        Yu Zhao <yuzhao@...gle.com>, Peter Xu <peterx@...hat.com>,
        Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v2] x86/vm86/32: Remove VM86_SCREEN_BITMAP support

19.01.2021 20:40, Andy Lutomirski пишет:
> The implementation was rather buggy.  It unconditionally marked PTEs
> read-only, even for VM_SHARED mappings.  I'm not sure whether this is
> actually a problem, but it certainly seems unwise.  More importantly, it
> released the mmap lock before flushing the TLB, which could allow a racing
> CoW operation to falsely believe that the underlying memory was not
> writable.
>
> I can't find any users at all of this mechanism, so just remove it.
>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Linux-MM <linux-mm@...ck.org>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: x86@...nel.org
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Yu Zhao <yuzhao@...gle.com>
> Cc: Peter Xu <peterx@...hat.com>
> Cc: Stas Sergeev <stsp@...t.ru>
> Cc: Brian Gerst <brgerst@...il.com>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
Acked-by: stsp2@...dex.ru

dosemu2 just uses mprotect().
The BIOSSEG stuff in vm86_32.c is also
unused btw.