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Re: [PATCH v2 03/27] staging: unisys: iovmcall_gnuc.h change -1 return values

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On Tue, May 31, 2016 at 10:26:29PM -0400, David Kershner wrote:
> From: Erik Arfvidson <erik.arfvidson@unisys.com>
> 
> This patch changes the vague -1 return values to -EPERM.
> This operation is not supported is a good alternative
> to -1 because the return is basically telling the caller
> that the processor doesn't support vmcall operations.
> 
> Signed-off-by: Erik Arfvidson <erik.arfvidson@unisys.com>
> Signed-off-by: David Kershner <david.kershner@unisys.com>
> Reviewed-by: Tim Sell <Timothy.Sell@unisys.com>
> ---
>  drivers/staging/unisys/visorbus/iovmcall_gnuc.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/unisys/visorbus/iovmcall_gnuc.h b/drivers/staging/unisys/visorbus/iovmcall_gnuc.h
> index b08b6ec..98ea7f3 100644
> --- a/drivers/staging/unisys/visorbus/iovmcall_gnuc.h
> +++ b/drivers/staging/unisys/visorbus/iovmcall_gnuc.h
> @@ -22,7 +22,7 @@ __unisys_vmcall_gnuc(unsigned long tuple, unsigned long reg_ebx,
>  
>  	cpuid(0x00000001, &cpuid_eax, &cpuid_ebx, &cpuid_ecx, &cpuid_edx);
>  	if (!(cpuid_ecx & 0x80000000))
> -		return -1;
> +		return -EPERM;
>  
>  	__asm__ __volatile__(".byte 0x00f, 0x001, 0x0c1" : "=a"(result) :
>  		"a"(tuple), "b"(reg_ebx), "c"(reg_ecx));
> @@ -40,7 +40,7 @@ __unisys_extended_vmcall_gnuc(unsigned long long tuple,
>  
>  	cpuid(0x00000001, &cpuid_eax, &cpuid_ebx, &cpuid_ecx, &cpuid_edx);
>  	if (!(cpuid_ecx & 0x80000000))
> -		return -1;
> +		return -EPERM;
>  
>  	__asm__ __volatile__(".byte 0x00f, 0x001, 0x0c1" : "=a"(result) :
>  		"a"(tuple), "b"(reg_ebx), "c"(reg_ecx), "d"(reg_edx));
> -- 
> 1.9.1
> 

This gets properly checked as far as return codes go for the most part, which is
good, but in the case of an issuing of the
VMCALL_QUERY_GUEST_VIRTUAL_TIME_OFFSET ioctl, the return code is simply copied
into a user space buffer.  That might be expected if -1 is used as an error
condition marker, but I would check before you assume that a user space caller
will handle -EINVAL properly there.

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[PATCH v2 00/27] Fixed issues raised by  tglx, then move visorbus to drivers/virt David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 13/27] staging: unisys: visorbus: Make visordriver_callback_lock a mutex David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
    Re: [PATCH v2 13/27] staging: unisys: visorbus: Make visordriver_callback_lock  a mutex Thomas Gleixner <tglx@linutronix.de> - 2016-06-01 08:50 +0200
  [PATCH v2 27/27] drivers: Add visorbus to the drivers directory David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 17/27] staging: unisys: visorbus: vbusdeviceinfo function descriptions more kerneldoc-like David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 12/27] staging: unisys: visorbus: remove periodic_work.h/.c David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 06/27] staging: unisys: visorbus: modify format string to match argument David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 16/27] staging: unisys: Remove reference to unused STANDALONE_CLIENT David Kershner <david.kershner@unisys.com> - 2016-06-01 04:30 +0200
  [PATCH v2 05/27] staging: unisys: visorbus: remove unused struct David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 07/27] staging: unisys: visornic: Correct comment spelling mistake David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 24/27] staging: unisys: Move vbushelper.h to visorbus directory David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary locking David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
    Re: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking Thomas Gleixner <tglx@linutronix.de> - 2016-06-01 08:50 +0200
      RE: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-06-03 06:40 +0200
    Re: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking Neil Horman <nhorman@redhat.com> - 2016-06-01 16:20 +0200
      RE: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-06-01 17:10 +0200
        Re: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking Neil Horman <nhorman@redhat.com> - 2016-06-01 20:50 +0200
          RE: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-06-02 07:10 +0200
            Re: [PATCH v2 10/27] staging: unisys: visorinput: remove unnecessary  locking Neil Horman <nhorman@redhat.com> - 2016-06-02 14:50 +0200
  [PATCH v2 15/27] staging: unisys: visorbus: Remove unused functions David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 20/27] staging: unisys: visorbus: make visorchannel function descriptions more kerneldoc-like David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
    Re: [PATCH v2 20/27] staging: unisys: visorbus: make visorchannel  function descriptions more kerneldoc-like Thomas Gleixner <tglx@linutronix.de> - 2016-06-01 08:50 +0200
  [PATCH v2 23/27] staging: unisys: visorbus: Add kerneldoc-style comments for visorbus API David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 04/27] staging: unisys: visorbus: remove unused module parameters David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 18/27] staging: unisys: visorbus: make function descriptions more kerneldoc-like David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 14/27] staging: unisys: visorbus: Remove unnecessary EXPORT_SYMBOL statements David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 02/27] staging: unisys: visorchipset change -1 return value David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
    Re: [PATCH v2 02/27] staging: unisys: visorchipset change -1 return  value Neil Horman <nhorman@redhat.com> - 2016-06-01 15:20 +0200
  [PATCH v2 08/27] staging: unisys: include: Remove thread-related enum members David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 22/27] staging: unisys: visorbus: Move visorbus-unique functions to private header David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 03/27] staging: unisys: iovmcall_gnuc.h change -1 return values David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
    Re: [PATCH v2 03/27] staging: unisys: iovmcall_gnuc.h change -1  return values Neil Horman <nhorman@redhat.com> - 2016-06-01 15:40 +0200
  [PATCH v2 21/27] staging: unisys: visorbus: make visorchipset function descriptions more kerneldoc-like David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 01/27] staging: unisys: visorbus change -1 return values David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
    Re: [PATCH v2 01/27] staging: unisys: visorbus change -1 return  values Neil Horman <nhorman@redhat.com> - 2016-06-01 15:30 +0200
  [PATCH v2 19/27] staging: unisys: visorbus: make visorbus_private.h function descriptions more kerneldoc-like David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 11/27] staging: unisys: visorbus: use kernel timer instead of workqueue David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200
  [PATCH v2 09/27] staging: unisys: visorbus: removed unused periodic_test_workqueue David Kershner <david.kershner@unisys.com> - 2016-06-01 04:40 +0200

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