Re: [PATCH v2 1/3] x86/xen: use clear_bss() for Xen PV guests

From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	xen-devel@lists.xenproject.org, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] x86/xen: use clear_bss() for Xen PV guests
Date: Thu, 23 Jun 2022 11:51:42 +0200	[thread overview]
Message-ID: <117fd526-a241-2f01-47b5-e40e1803124b@suse.com> (raw)
In-Reply-To: <20220623094608.7294-2-jgross@suse.com>

On 23.06.2022 11:46, Juergen Gross wrote:
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1183,15 +1183,19 @@ static void __init xen_domu_set_legacy_features(void)
>  extern void early_xen_iret_patch(void);
>  
>  /* First C function to be called on Xen boot */
> -asmlinkage __visible void __init xen_start_kernel(void)
> +asmlinkage __visible void __init xen_start_kernel(struct start_info *si)
>  {
>  	struct physdev_set_iopl set_iopl;
>  	unsigned long initrd_start = 0;
>  	int rc;
>  
> -	if (!xen_start_info)
> +	if (!si)
>  		return;
>  
> +	clear_bss();

As per subsequent observation, this shouldn't really be needed: The
hypervisor (or tool stack for DomU-s) already does so. While I guess
we want to keep it to be on the safe side, maybe worth a comment?

Jan