Re: [Qemu-devel] [PATCH 1/2] [RFC] Make vmport report the processor speed

[Anthony Liguori <anthony@codemonkey.ws>]

Alexander Graf wrote:
> If VMware ESX finds itself virtualized (read: inside VMware), it reads the TSC speed
> from its backdoor, because measuring the TSC inside a VM is not exact.
>
> This patch implements a hacky way to detect the TSC speed and passes that through to
> the VM. I am open to suggestions on how to improve the behavior.
> It also adds a magic return value of 2 on the version return, which is required by
> VMware ESX.
>
> WARNING: This implementation breaks on non-x86 hosts!
>   

BTW, this is very broken because of CPU migration or TSC frequency 
scaling.  In general, there's no way to do this correctly from 
userspace.  Looking at /proc/cpuinfo bogomips is probably more accurate.

Regards,

Anthony Liguori

> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  hw/vmport.c |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/hw/vmport.c b/hw/vmport.c
> index 884af3f..825fd92 100644
> --- a/hw/vmport.c
> +++ b/hw/vmport.c
> @@ -28,6 +28,7 @@
>  
>  //#define VMPORT_DEBUG
>  
> +#define VMPORT_CMD_GETPROCSPEED 0x01
>  #define VMPORT_CMD_GETVERSION 0x0a
>  #define VMPORT_CMD_GETRAMSIZE 0x14
>  
> @@ -87,6 +88,7 @@ static uint32_t vmport_cmd_get_version(void *opaque, uint32_t addr)
>  {
>      CPUState *env = cpu_single_env;
>      env->regs[R_EBX] = VMPORT_MAGIC;
> +    env->regs[R_ECX] = 2;
>      return 6;
>  }
>  
> @@ -97,6 +99,25 @@ static uint32_t vmport_cmd_ram_size(void *opaque, uint32_t addr)
>      return ram_size;
>  }
>  
> +
> +static inline int64_t rdtsc(void)
> +{
> +    int64_t val;
> +    asm volatile ("rdtsc" : "=A" (val));
> +    return val;
> +}
> +
> +static uint32_t vmport_cmd_proc_speed(void *opaque, uint32_t addr)
> +{
> +    static uint64_t tsc = 0;
> +    if ( tsc == 0 ) {
> +        tsc = rdtsc();
> +        usleep(100000);
> +        tsc = (rdtsc() - tsc) / 100000;
> +    }
> +    return (tsc / 66) * 66;
> +}
> +
>  void vmport_init(void)
>  {
>      register_ioport_read(0x5658, 1, 4, vmport_ioport_read, &port_state);
> @@ -105,4 +126,5 @@ void vmport_init(void)
>      /* Register some generic port commands */
>      vmport_register(VMPORT_CMD_GETVERSION, vmport_cmd_get_version, NULL);
>      vmport_register(VMPORT_CMD_GETRAMSIZE, vmport_cmd_ram_size, NULL);
> +    vmport_register(VMPORT_CMD_GETPROCSPEED, vmport_cmd_proc_speed, NULL);
>  }
>