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

[Dave Hansen]

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().