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Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops

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* Andy Lutomirski <luto@kernel.org> wrote:

> Setting CONFIG_PARAVIRT=y has an unintended side effect: it silently
> turns all rdmsr and wrmsr operations into the safe variants without
> any checks that the operations actually succeed.
> 
> This is IMO awful: it papers over bugs.  In particular, KVM gueests
> might be unwittingly depending on this behavior because
> CONFIG_KVM_GUEST currently depends on CONFIG_PARAVIRT.  I'm not
> aware of any such problems, but applying this series would be a good
> way to shake them out.
> 
> Fix it so that the MSR operations work the same on CONFIG_PARAVIRT=n
> and CONFIG_PARAVIRT=y as long as Xen isn't being used.  The Xen
> maintainers are welcome to make a similar change on top of this.
> 
> Since there's plenty of time before the next merge window, I think
> we should apply and fix anything that breaks.

No, I think we should at most generate a warning instead, and not crash the kernel 
via rdmsr()!

Most big distro kernels on bare metal have CONFIG_PARAVIRT=y (I checked Ubuntu and 
Fedora), so we are potentially exposing a lot of users to problems.

Crashing the bootup on an unknown MSR is bad. Many MSR reads and writes are 
non-critical and returning the 'safe' result is much better than crashing or 
hanging the bootup.

( We should double check that rdmsr()/wrmsr() results are never left 
  uninitialized, but are set to zero or so, for cases where the return code is not 
  checked. )

Thanks,

	Ingo
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[PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski <luto@kernel.org> - 2015-09-17 01:40 +0200
  [PATCH 3/3] x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y Andy Lutomirski <luto@kernel.org> - 2015-09-17 01:40 +0200
  Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Ingo Molnar <mingo@kernel.org> - 2015-09-17 09:20 +0200
    Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Borislav Petkov <bp@alien8.de> - 2015-09-17 11:40 +0200
      Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops "H. Peter Anvin" <hpa@zytor.com> - 2015-09-17 13:30 +0200
      Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-17 13:40 +0200
        Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Borislav Petkov <bp@alien8.de> - 2015-09-17 17:30 +0200
          Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR  ops Borislav Petkov <bp@alien8.de> - 2015-09-17 17:40 +0200
          Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt  MSR ops Andrew Cooper <andrew.cooper3@citrix.com> - 2015-09-17 17:40 +0200
    Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Arjan van de Ven <arjan@linux.intel.com> - 2015-09-17 17:30 +0200
      Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-17 17:30 +0200
        Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Arjan van de Ven <arjan@linux.intel.com> - 2015-09-17 17:40 +0200
          Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-17 17:40 +0200
    Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski <luto@amacapital.net> - 2015-09-17 17:30 +0200
      Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Ingo Molnar <mingo@kernel.org> - 2015-09-17 19:40 +0200
        Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski <luto@amacapital.net> - 2015-09-17 21:00 +0200
  Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Peter Zijlstra <peterz@infradead.org> - 2015-09-17 11:10 +0200
    Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-17 13:50 +0200
      Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Peter Zijlstra <peterz@infradead.org> - 2015-09-17 14:40 +0200
        Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski <luto@amacapital.net> - 2015-09-17 17:20 +0200
          Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Peter Zijlstra <peterz@infradead.org> - 2015-09-17 17:30 +0200
            Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski <luto@amacapital.net> - 2015-09-17 17:30 +0200
              Re: [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-17 17:40 +0200
  Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt  MSR ops Andrew Cooper <andrew.cooper3@citrix.com> - 2015-09-17 11:20 +0200
    Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt  MSR ops Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2015-09-17 17:20 +0200

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