Re: [Xen-devel] [PATCH for-next v2 9/9] x86: introduce CONFIG_HYPERV and detection code

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Oct 21, 2019 at 12:22:25PM +0200, Roger Pau Monné wrote:
> On Mon, Sep 30, 2019 at 04:00:43PM +0100, Wei Liu wrote:
> > We use the same code structure as we die for Xen.
> > 
> > As starters, detect Hyper-V in probe routine. More complex
> > functionalities will be added later.
> > 
> > Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> > ---
> >  xen/arch/x86/Kconfig               |  9 ++++
> >  xen/arch/x86/guest/Makefile        |  1 +
> >  xen/arch/x86/guest/hyperv/Makefile |  1 +
> >  xen/arch/x86/guest/hyperv/hyperv.c | 69 ++++++++++++++++++++++++++++++
> >  xen/arch/x86/guest/hypervisor.c    |  5 +++
> >  xen/include/asm-x86/guest.h        |  1 +
> >  xen/include/asm-x86/guest/hyperv.h | 45 +++++++++++++++++++
> >  7 files changed, 131 insertions(+)
> >  create mode 100644 xen/arch/x86/guest/hyperv/Makefile
> >  create mode 100644 xen/arch/x86/guest/hyperv/hyperv.c
> >  create mode 100644 xen/include/asm-x86/guest/hyperv.h
> > 
> > diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> > index 584bdc1bb8..c5a93babfe 100644
> > --- a/xen/arch/x86/Kconfig
> > +++ b/xen/arch/x86/Kconfig
> > @@ -163,6 +163,15 @@ endchoice
> >  config GUEST
> >     bool
> >  
> > +config HYPERV_GUEST
> > +   def_bool n
> > +   select GUEST
> > +   prompt "Hyper-V Guest"
> > +   ---help---
> > +     Support for Xen detecting when it is running under Hyper-V.
> > +
> > +     If unsure, say N.
> > +
> >  config XEN_GUEST
> >     def_bool n
> >     select GUEST
> > diff --git a/xen/arch/x86/guest/Makefile b/xen/arch/x86/guest/Makefile
> > index f63d64bbee..f164196772 100644
> > --- a/xen/arch/x86/guest/Makefile
> > +++ b/xen/arch/x86/guest/Makefile
> > @@ -1,3 +1,4 @@
> >  obj-y += hypervisor.o
> >  
> > +subdir-$(CONFIG_HYPERV_GUEST) += hyperv
> >  subdir-$(CONFIG_XEN_GUEST) += xen
> > diff --git a/xen/arch/x86/guest/hyperv/Makefile 
> > b/xen/arch/x86/guest/hyperv/Makefile
> > new file mode 100644
> > index 0000000000..68170109a9
> > --- /dev/null
> > +++ b/xen/arch/x86/guest/hyperv/Makefile
> > @@ -0,0 +1 @@
> > +obj-y += hyperv.o
> > diff --git a/xen/arch/x86/guest/hyperv/hyperv.c 
> > b/xen/arch/x86/guest/hyperv/hyperv.c
> > new file mode 100644
> > index 0000000000..4494b87fe8
> > --- /dev/null
> > +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> > @@ -0,0 +1,69 @@
> > +/******************************************************************************
> > + * arch/x86/guest/hyperv/hyperv.c
> > + *
> > + * Support for detecting and running under Hyper-V.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; If not, see <http://www.gnu.org/licenses/>.
> > + *
> > + * Copyright (c) 2019 Microsoft.
> > + */
> > +#include <xen/init.h>
> > +
> > +#include <asm/guest.h>
> > +
> > +bool __init hyperv_probe(void)
> > +{
> > +    uint32_t eax, ebx, ecx, edx;
> > +    bool hyperv_guest = false;
> 
> I don't think you need this local variable, you can return true in if
> the if condition matches, and false otherwise.
> 
> > +
> > +    cpuid(0x40000000, &eax, &ebx, &ecx, &edx);
> > +    if ( (ebx == 0x7263694d) && /* "Micr" */
> > +         (ecx == 0x666f736f) && /* "osof" */
> > +         (edx == 0x76482074) )  /* "t Hv" */
> 
> I guess there are no HyperV headers to import that have those values
> defined?
> 
> Alternatively you could do something like the following I think:
> 
> static const char hyperv_sig[] __initconst = "Microsoft Hv";
> 
> bool __init hyperv_probe(void)
> {
>     uint32_t eax, sig[3];
> 
>     cpuid(0x40000000, &eax, &sig[0], &sig[1], &sig[2]);
>     if ( !strncmp(hyperv_sig, sig, strncmp(hyperv_sig) )

Urg, I've made a mistake here, the line should be:

!strncmp(hyperv_sig, sig, strlen(hyperv_sig))

And you can likely declare hyperv_sig inside the probe function also.

Roger.

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