Re: [PATCH 4.19 49/49] x86/Xen: swap NX determination and GDT setup on BSP

[Juergen Gross]

On 24.05.21 17:26, Greg Kroah-Hartman wrote:
> From: Jan Beulich <jbeulich@xxxxxxxx>
>
> commit ae897fda4f507e4b239f0bdfd578b3688ca96fb4 upstream.
>
> 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.
>
> [jgross] Note that this is a revert of 36104cb9012a82e73 ("x86/xen:
> Delay get_cpu_cap until stack canary is established"), which is possible
> now that we no longer support running as PV guest in 32-bit mode.
>
> 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 canary is established")
> Reported-by: Olaf Hering <olaf@xxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>
> Link: https://lore.kernel.org/r/12a866b0-9e89-59f7-ebeb-a2a6cec0987a@xxxxxxxx
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>   arch/x86/xen/enlighten_pv.c |    8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> --- 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();
>   
> +	/* 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);
>   
> -	/* 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);
>

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