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

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On 17/09/15 00:33, Andy Lutomirski 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.

The Xen side of things need some further modification before this would
be a safe operation to perform.

On the wrmsr side of things alone, this is the list of things Xen
currently objects to and injects #GP faults for.

(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000081 from
0xe023e00800000000 to 0x0023001000000000.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000082 from
0xffff82d0bffff000 to 0xffffffff81560060.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000083 from
0xffff82d0bffff020 to 0xffffffff81558100.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000174 from
0x000000000000e008 to 0x0000000000000010.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000175 from
0xffff8300ac0f7fc0 to 0x0000000000000000.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000176 from
0xffff82d08023fd50 to 0xffffffff815616d0.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000083 from
0xffff82d0bffff020 to 0xffffffff81561910.
(XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000084 from
0x0000000000074700 to 0x0000000000047700.

However, it would be certainly be worth teaching PVops not to play with
MSRs it doesn't own.

~Andrew
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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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