Re: [PATCH v2] KVM: x86: use wrpkru directly in kvm_load_{guest|host}_xsave_state

[Paolo Bonzini]

On 11/05/21 18:45, Dave Hansen wrote:
> On 5/11/21 8:59 AM, Jon Kohler wrote:
> > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> > index b1099f2d9800..20f1fb8be7ef 100644
> > --- a/arch/x86/include/asm/pgtable.h
> > +++ b/arch/x86/include/asm/pgtable.h
> > @@ -151,7 +151,7 @@ static inline void write_pkru(u32 pkru)
> >   	fpregs_lock();
> >   	if (pk)
> >   		pk->pkru = pkru;
> > -	__write_pkru(pkru);
> > +	wrpkru(pkru);
> >   	fpregs_unlock();
> >   }
>
> This removes the:
>
> 	if (pkru == rdpkru())
> 		return;
>
> optimization from a couple of write_pkru() users:
> arch_set_user_pkey_access() and copy_init_pkru_to_fpregs().
>
> Was that intentional?  Those aren't the hottest paths in the kernel, but
> copy_init_pkru_to_fpregs() is used in signal handling and exeve().

Yeah, you should move it from __write_pkru() to write_pkru() but not 
remove it completely.

Paolo