Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled
Date	2015-09-29 22:40 +0200
Message-ID	<qe9QR-oL-7@gated-at.bofh.it> (permalink)
References	(4 earlier) <qdG2u-5Zh-21@gated-at.bofh.it> <qdZ58-1ZA-13@gated-at.bofh.it> <qe72H-4PH-19@gated-at.bofh.it> <qe7m2-5cj-13@gated-at.bofh.it> <qe7vI-5CQ-7@gated-at.bofh.it>
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On 09/29/2015 11:02 AM, Andy Lutomirski wrote:
> On Tue, Sep 29, 2015 at 10:50 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>
>>> Does anyone know what happens if you stick a non-accessed segment in
>>> the GDT, map the GDT RO, and access it?
>>
>> You should get a #PF, as you guess, but go ahead and test it if you
>> want to make sure.
> 
> Then I think that, if we do this, the patch series should first make
> it percpu and fixmapped but RW and then flip it RO as a separate patch
> in case we need to revert the actual RO bit.  I don't want to break
> Wine or The Witcher 2 because of this, and we might need various
> fixups.  I really hope that no one uses get_thread_area to check
> whether TLS has been accessed.
> 

Of course.

	-hpa


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Thread

[PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Denys Vlasenko <dvlasenk@redhat.com> - 2015-09-26 20:10 +0200
  Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-26 22:00 +0200
    Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Denys Vlasenko <dvlasenk@redhat.com> - 2015-09-26 22:40 +0200
      Re: [PATCH] x86: Use entire page for the per-cpu GDT only if  paravirt-enabled Ingo Molnar <mingo@kernel.org> - 2015-09-28 10:00 +0200
        Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Denys Vlasenko <dvlasenk@redhat.com> - 2015-09-28 14:50 +0200
          Re: [PATCH] x86: Use entire page for the per-cpu GDT only if  paravirt-enabled Ingo Molnar <mingo@kernel.org> - 2015-09-29 11:10 +0200
            Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Andy Lutomirski <luto@amacapital.net> - 2015-09-29 19:40 +0200
              Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-29 20:00 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Andy Lutomirski <luto@amacapital.net> - 2015-09-29 20:10 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if  paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-29 22:40 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled ebiederm@xmission.com (Eric W. Biederman) - 2015-09-30 03:30 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if  paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 03:40 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled ebiederm@xmission.com (Eric W. Biederman) - 2015-09-30 04:20 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 04:30 +0200
              Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-29 20:30 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled "H. Peter Anvin" <hpa@zytor.com> - 2015-09-29 20:30 +0200
                Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Andy Lutomirski <luto@amacapital.net> - 2015-09-29 20:30 +0200

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