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Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to zero

From Borislav Petkov <bp@alien8.de>
Newsgroups linux.kernel
Subject Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to zero
Date 2017-04-25 21:20 +0200
Message-ID <tAead-kQ-13@gated-at.bofh.it> (permalink)
References <tAd4t-84X-3@gated-at.bofh.it> <tAdnQ-8d5-39@gated-at.bofh.it> <tAdxw-8iW-47@gated-at.bofh.it>
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On Tue, Apr 25, 2017 at 08:34:34PM +0200, Juergen Gross wrote:
> And what happens when there is a scheduling event right here?
> __switch_to() will see X86_BUG_SYSRET_SS_ATTRS set and take a wrong
> path.

So the whole thing we're doing right now is wrong: set bit and then
clear bit.

We should not set the bit at all and there won't be any window to get it
wrong.

So can we do something like this instead:

	if (!cpu_has(c, X86_FEATURE_XENPV))
		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);

or is XENPV the wrong thing to test?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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[PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to zero Juergen Gross <jgross@suse.com> - 2017-04-25 20:10 +0200
  Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Borislav Petkov <bp@alien8.de> - 2017-04-25 20:30 +0200
    Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Juergen Gross <jgross@suse.com> - 2017-04-25 20:40 +0200
      Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Borislav Petkov <bp@alien8.de> - 2017-04-25 21:20 +0200
        Re: [Xen-devel] [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if  forced to zero Andrew Cooper <andrew.cooper3@citrix.com> - 2017-04-25 22:20 +0200
          Re: [Xen-devel] [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS  if forced to zero Borislav Petkov <bp@alien8.de> - 2017-04-25 22:30 +0200
        Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Juergen Gross <jgross@suse.com> - 2017-04-26 06:50 +0200
          Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Borislav Petkov <bp@alien8.de> - 2017-04-26 08:40 +0200
            Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Juergen Gross <jgross@suse.com> - 2017-04-26 20:30 +0200
              Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Borislav Petkov <bp@alien8.de> - 2017-04-27 00:10 +0200
                Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to  zero Juergen Gross <jgross@suse.com> - 2017-04-27 06:50 +0200

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