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

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

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) )
        return true;

    return false;
}

> +        hyperv_guest = true;
> +
> +    return hyperv_guest;
> +}
> +
> +void __init hyperv_setup(void)
> +{
> +    /* Nothing yet */
> +}
> +
> +void hyperv_ap_setup(void)
> +{
> +    /* Nothing yet */
> +}
> +
> +void hyperv_resume(void)
> +{
> +    /* Nothing yet */
> +}

There's no need to introduce such dummy functions, just leaving the
pointers as NULL should work fine, and the functions can be introduced
when there's logic in them.

> +
> +struct hypervisor_ops hyperv_hypervisor_ops = {
> +    .name = "Hyper-V",
> +    .setup = hyperv_setup,
> +    .ap_setup = hyperv_ap_setup,
> +    .resume = hyperv_resume,
> +};
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/arch/x86/guest/hypervisor.c b/xen/arch/x86/guest/hypervisor.c
> index 8161b26c5a..87a195e888 100644
> --- a/xen/arch/x86/guest/hypervisor.c
> +++ b/xen/arch/x86/guest/hypervisor.c
> @@ -40,6 +40,11 @@ bool hypervisor_probe(void)
>          hops = &xen_hypervisor_ops;
>  #endif
>  
> +#ifdef CONFIG_HYPERV_GUEST
> +    if ( hyperv_probe() )
> +        hops = &hyperv_hypervisor_ops;
> +#endif

This won't work correctly if Xen has viridian extensions enabled,
since the HyperV probe will overwrite the Xen one.

> +
>      return !!hops;
>  }
>  
> diff --git a/xen/include/asm-x86/guest.h b/xen/include/asm-x86/guest.h
> index 8e167165ae..94448606d4 100644
> --- a/xen/include/asm-x86/guest.h
> +++ b/xen/include/asm-x86/guest.h
> @@ -20,6 +20,7 @@
>  #define __X86_GUEST_H__
>  
>  #include <asm/guest/hypercall.h>
> +#include <asm/guest/hyperv.h>
>  #include <asm/guest/hypervisor.h>
>  #include <asm/guest/pvh-boot.h>
>  #include <asm/guest/xen.h>
> diff --git a/xen/include/asm-x86/guest/hyperv.h 
> b/xen/include/asm-x86/guest/hyperv.h
> new file mode 100644
> index 0000000000..a2d8ee8987
> --- /dev/null
> +++ b/xen/include/asm-x86/guest/hyperv.h
> @@ -0,0 +1,45 @@
> +/******************************************************************************
> + * asm-x86/guest/hyperv.h
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms and conditions of the GNU General Public
> + * License, version 2, as published by the Free Software Foundation.
> + *
> + * 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.
> + */
> +
> +#ifndef __X86_GUEST_HYPERV_H__
> +#define __X86_GUEST_HYPERV_H__
> +
> +#ifdef CONFIG_HYPERV_GUEST
> +
> +#include <asm/guest/hypervisor.h>
> +
> +extern struct hypervisor_ops hyperv_hypervisor_ops;

hyperv_ops would be fine by me, seems kind of redundant to have
'hyper' twice in a name.

Thanks, Roger.

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