Re: [Xen-devel] [PATCH for-next v3 9/9] x86: introduce CONFIG_HYPERV and detection code

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.10.2019 17:57, Wei Liu wrote:
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -164,6 +164,15 @@ endchoice
>  config GUEST
>       bool
>  
> +config HYPERV_GUEST
> +     def_bool n
> +     select GUEST
> +     prompt "Hyper-V Guest"

Please can you avoid following the bad example XEN_GUEST gives (and
perhaps even take the opportunity here or in the earlier patch
adding GUEST to change that one as well)? What you want is

config HYPERV_GUEST
        bool "Hyper-V Guest"
        select GUEST

> --- /dev/null
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -0,0 +1,54 @@
> +/******************************************************************************
> + * 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;
> +
> +    cpuid(0x40000000, &eax, &ebx, &ecx, &edx);
> +    if ( !((ebx == 0x7263694d) &&  /* "Micr" */
> +           (ecx == 0x666f736f) &&  /* "osof" */
> +           (edx == 0x76482074)) )  /* "t Hv" */
> +        return false;
> +
> +    cpuid(0x40000001, &eax, &ebx, &ecx, &edx);
> +    if ( eax != 0x31237648 )    /* Hv#1 */
> +        return false;
> +
> +    return true;
> +}
> +
> +struct hypervisor_ops hyperv_ops = {

const again.

> --- a/xen/arch/x86/guest/hypervisor.c
> +++ b/xen/arch/x86/guest/hypervisor.c
> @@ -43,6 +43,14 @@ bool hypervisor_probe(void)
>      }
>  #endif
>  
> +#ifdef CONFIG_HYPERV_GUEST
> +    if ( hyperv_probe() )
> +    {
> +        hops = &hyperv_ops;
> +        return true;
> +    }
> +#endif

This recurring #ifdef CONFIG_*_GUEST is going to start looking ugly
the latest when one or two more get added. Perhaps better providing
*_probe() stubs returning false, and (like we do elsewhere) rely on
DCE to get rid of the *_ops reference? (And really you already have
such a stub - all you need to do is put the hyperv_ops declaration
outside the #ifdef (but read on).

Also how about having *_probe() return the address of *_ops, such
that the latter could all become static?

Jan

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