RE: [PATCH] x86: guest: rely on leaf 0x40000001 to detect Hyper-V

[KY Srinivasan]

> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo
> Bonzini
> Sent: Friday, October 2, 2015 2:27 AM
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; x86@xxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> alex.williamson@xxxxxxxxxx
> Subject: [PATCH] x86: guest: rely on leaf 0x40000001 to detect Hyper-V
> 
> The specification says that "Microsoft Hv" is actually a vendor ID field
> that is only used for reporting and diagnostic purposes.  The actual
> field that you need to check is the interface ID that you get in eax
> when querying the HYPERV_CPUID_INTERFACE.
> 
> Change ms_hyperv_platform to actually do what the specification suggests.
> This roughy matches what Windows looks for, though Windows actually
> ignores HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS completely.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Thanks Paolo.

Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c
> b/arch/x86/kernel/cpu/mshyperv.c
> index 381c8b9b3a33..7910e7fd705b 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -116,18 +116,16 @@ static void hv_machine_crash_shutdown(struct
> pt_regs *regs)
>  static uint32_t  __init ms_hyperv_platform(void)
>  {
>  	u32 eax;
> -	u32 hyp_signature[3];
> 
>  	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
>  		return 0;
> 
> -	cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
> -	      &eax, &hyp_signature[0], &hyp_signature[1],
> &hyp_signature[2]);
> -
> -	if (eax >= HYPERV_CPUID_MIN &&
> -	    eax <= HYPERV_CPUID_MAX &&
> -	    !memcmp("Microsoft Hv", hyp_signature, 12))
> -		return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
> +	eax =
> cpuid_eax(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS);
> +	if (eax >= HYPERV_CPUID_MIN && eax <= HYPERV_CPUID_MAX) {
> +		eax = cpuid_eax(HYPERV_CPUID_INTERFACE);
> +		if (!memcmp(&eax, "Hv#1", sizeof(eax)))
> +			return
> HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
> +	}
> 
>  	return 0;
>  }
> --
> 2.5.0

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