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Subject: Re: [PATCH 4.19 49/49] x86/Xen: swap NX determination and GDT setup
 on BSP
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     stable@vger.kernel.org, Olaf Hering <olaf@aepfle.de>,
        Jan Beulich <jbeulich@suse.com>
References: <20210524152324.382084875@linuxfoundation.org>
 <20210524152325.958181984@linuxfoundation.org>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <bdadfa45-0496-9d47-cca0-b0839b811ae9@suse.com>
Date:   Tue, 25 May 2021 07:11:21 +0200
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From: Juergen Gross <jgross@suse.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org, Olaf Hering <olaf@aepfle.de>,
 Jan Beulich <jbeulich@suse.com>
Message-ID: <bdadfa45-0496-9d47-cca0-b0839b811ae9@suse.com>
Subject: Re: [PATCH 4.19 49/49] x86/Xen: swap NX determination and GDT setup
 on BSP
References: <20210524152324.382084875@linuxfoundation.org>
 <20210524152325.958181984@linuxfoundation.org>
In-Reply-To: <20210524152325.958181984@linuxfoundation.org>

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On 24.05.21 17:26, Greg Kroah-Hartman wrote:
> From: Jan Beulich <jbeulich@suse.com>
>=20
> commit ae897fda4f507e4b239f0bdfd578b3688ca96fb4 upstream.
>=20
> xen_setup_gdt(), via xen_load_gdt_boot(), wants to adjust page tables.
> For this to work when NX is not available, x86_configure_nx() needs to
> be called first.
>=20
> [jgross] Note that this is a revert of 36104cb9012a82e73 ("x86/xen:
> Delay get_cpu_cap until stack canary is established"), which is possibl=
e
> now that we no longer support running as PV guest in 32-bit mode.
>=20
> Cc: <stable.vger.kernel.org> # 5.9

Sorry for messing up the stable link, but please don't include this
patch in stable kernels before 5.9


Juergen

> Fixes: 36104cb9012a82e73 ("x86/xen: Delay get_cpu_cap until stack canar=
y is established")
> Reported-by: Olaf Hering <olaf@aepfle.de>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Juergen Gross <jgross@suse.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>=20
> Link: https://lore.kernel.org/r/12a866b0-9e89-59f7-ebeb-a2a6cec0987a@su=
se.com
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>   arch/x86/xen/enlighten_pv.c |    8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>=20
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1246,16 +1246,16 @@ asmlinkage __visible void __init xen_sta
>   	/* Get mfn list */
>   	xen_build_dynamic_phys_to_machine();
>  =20
> +	/* Work out if we support NX */
> +	get_cpu_cap(&boot_cpu_data);
> +	x86_configure_nx();
> +
>   	/*
>   	 * Set up kernel GDT and segment registers, mainly so that
>   	 * -fstack-protector code can be executed.
>   	 */
>   	xen_setup_gdt(0);
>  =20
> -	/* Work out if we support NX */
> -	get_cpu_cap(&boot_cpu_data);
> -	x86_configure_nx();
> -
>   	/* Determine virtual and physical address sizes */
>   	get_cpu_address_sizes(&boot_cpu_data);
>  =20
>=20
>=20


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