Re: [Xen-devel] [PATCH for-next v2 8/9] x86: be more verbose when running on a hypervisor

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

On Mon, Sep 30, 2019 at 04:00:42PM +0100, Wei Liu wrote:
> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> ---
>  xen/arch/x86/guest/hypervisor.c        | 5 +++++
>  xen/arch/x86/setup.c                   | 6 +++++-
>  xen/include/asm-x86/guest/hypervisor.h | 2 ++
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/guest/hypervisor.c b/xen/arch/x86/guest/hypervisor.c
> index 30453b6a7a..8161b26c5a 100644
> --- a/xen/arch/x86/guest/hypervisor.c
> +++ b/xen/arch/x86/guest/hypervisor.c
> @@ -43,6 +43,11 @@ bool hypervisor_probe(void)
>      return !!hops;
>  }
>  
> +const char *hypervisor_name(void)
> +{

I would maybe add ASSERT(hops);

> +    return hops->name;
> +}
> +
>  void hypervisor_setup(void)
>  {
>      if ( hops && hops->setup )
> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index 0ee11b15a6..cf5a7b8e1e 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -689,6 +689,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>      int i, j, e820_warn = 0, bytes = 0;
>      bool acpi_boot_table_init_done = false, relocated = false;
>      int ret;
> +    bool running_on_hypervisor;
>      struct ns16550_defaults ns16550 = {
>          .data_bits = 8,
>          .parity    = 'n',
> @@ -763,7 +764,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>       * allocing any xenheap structures wanted in lower memory. */
>      kexec_early_calculations();
>  
> -    hypervisor_probe();
> +    running_on_hypervisor = hypervisor_probe();
>  
>      parse_video_info();
>  
> @@ -789,6 +790,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>  
>      printk("Xen image load base address: %#lx\n", xen_phys_start);
>  
> +    if ( running_on_hypervisor )
> +        printk("Running on %s\n", hypervisor_name());
> +
>  #ifdef CONFIG_VIDEO
>      printk("Video information:\n");
>  
> diff --git a/xen/include/asm-x86/guest/hypervisor.h 
> b/xen/include/asm-x86/guest/hypervisor.h
> index 38344e2e89..a7d75bf9cf 100644
> --- a/xen/include/asm-x86/guest/hypervisor.h
> +++ b/xen/include/asm-x86/guest/hypervisor.h
> @@ -36,6 +36,7 @@ bool hypervisor_probe(void);
>  void hypervisor_setup(void);
>  void hypervisor_ap_setup(void);
>  void hypervisor_resume(void);
> +const char *hypervisor_name(void);
>  
>  #else
>  
> @@ -45,6 +46,7 @@ static inline bool hypervisor_probe(void) { return false; }
>  static inline void hypervisor_setup(void) {}
>  static inline void hypervisor_ap_setup(void) {}
>  static inline void hypervisor_resume(void) {}
> +static inline char *hypervisor_name(void) { return NULL; }

I think you want an ASSERT_UNREACHABLE here, since hypervisor_name
shouldn't be called unless Xen has detected that's running as a guest,
which can only happen if CONFIG_GUEST is selected.

Thanks, Roger.

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