On Mon, May 20, 2013 at 8:59 PM, Theo de Raadt <dera...@cvs.openbsd.org> wrote:
>> On Mon, May 20, 2013 at 8:42 PM, Mike Larkin <mlar...@azathoth.net> wrote:
>> > On Mon, May 20, 2013 at 05:11:35PM +0000, Alexey E. Suslikov wrote:
>> >> Theo de Raadt <deraadt <at> cvs.openbsd.org> writes:
>> >>
>> >> > If these VM's are real VM's the should start emulating the machines
>> >> > they claim to be emulating correctly, or they should start advertising
>> >> > that they are something "different", so that we can isolate the bullshit
>> >> > factor.
>> >>
>> >> Ok. I see.
>> >>
>> >> Could we trim that down to the following?
>> >>
>> >> --- sys/arch/amd64/amd64/identcpu.c.orig Mon May 20 19:58:06 2013
>> >> +++ sys/arch/amd64/amd64/identcpu.c Mon May 20 20:01:08 2013
>> >> @@ -127,6 +127,7 @@
>> >> { CPUIDECX_AVX, "AVX" },
>> >> { CPUIDECX_F16C, "F16C" },
>> >> { CPUIDECX_RDRAND, "RDRAND" },
>> >> + { CPUIDECX_HV, "HV" },
>> >> }, cpu_ecpuid_ecxfeatures[] = {
>> >> { CPUIDECX_LAHF, "LAHF" },
>> >> { CPUIDECX_CMPLEG, "CMPLEG" },
>> >> --- sys/arch/amd64/include/specialreg.h.orig Mon May 20 20:01:56 2013
>> >> +++ sys/arch/amd64/include/specialreg.h Mon May 20 20:06:09 2013
>> >> @@ -158,6 +158,7 @@
>> >> #define CPUIDECX_AVX 0x10000000 /* Advanced Vector
>> >> Extensions */
>> >> #define CPUIDECX_F16C 0x20000000 /* 16bit fp conversion */
>> >> #define CPUIDECX_RDRAND 0x40000000 /* RDRAND instruction */
>> >> +#define CPUIDECX_HV 0x80000000 /* Hypervisor
>> >> presence */
>> >>
>> >> /*
>> >> * "Structured Extended Feature Flags Parameters" (CPUID function 0x7,
>> >> leaf 0)
>> >>
>> >
>> > That's certainly less objectionable but I'm not sure what useful
>> > information
>> > this diff provides.
>>
>> Seen in dmesg, HV flag will indicate operating system is run under hypervisor
>> and weird things are possible while running kernel code which depends on CPU
>> features.
>>
>> After all, it is kinda documented by AMD on page 570 of
>> http://support.amd.com/us/Processor_TechDocs/24594_APM_v3.pdf
>>
>> (AMD named it RAZ, but I put meaningful name like in FreeBSD - should we
>> put a reference to above mentioned document near the define?).
>
> Your statements here are trying to convince us of something which is
> false.
>
> AMD says "RAZ. Reserved for use by hypervisor to indicate guest status."
>
> That sentence does not translate to "The hypervisor is heavily broken
> and fails to completely emulate the machine otherwise advertised by
> the rest of the CPUID fields".
>
> It does not indicate that weird things are possible. If those weird
> things are possible, it is not because the hardware is broken, but
> because the *emulation of the hardware* by the VM is broken!
You misunderstood my point.
I'm not trying to convince, but avoid useless work/talk in the future:
* if one will see a *similar* bug report with a dmesg containing RAZ flag,
there will be no need for something to explore - it's a 99% broken VM.
