RE: [PATCH 43/61] KVM: x86: Use KVM cpu caps to mark CR4.LA57 as not-reserved

[David Laight]

From: Paolo Bonzini
> Sent: 25 February 2020 15:12
> On 24/02/20 23:08, Vitaly Kuznetsov wrote:
> >> +
> >> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> >> +{
> >> +	return kvm_cpu_cap_get(x86_feature);
> >> +}
> > I know this works (and I even checked C99 to make sure that it works not
> > by accident) but I have to admit that explicit '!!' conversion to bool
> > always makes me feel safer :-)
> 
> Same here, I don't really like the automagic bool behavior...

I just dislike 'bool'.

Conversion of 0/non-zero to 0/1 isn't completely free.
And something has to 'give' when the referenced memory location
doesn't contain 0 or 1.

One very old version of gcc made a complete hash of:
	bool_var |= function_returning_bool();

I'm not sure what the standard requires nor what current gcc
generates - but you want a 'logical or' instruction.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)