Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

[Thomas Gleixner]

On Fri, 10 Nov 2017, Dave Hansen wrote:
>  	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
> +
> +	/* CPU 0's mapping is done in kaiser_init() */
> +	if (cpu) {
> +		int ret;
> +
> +		ret = kaiser_add_mapping((unsigned long) get_cpu_gdt_ro(cpu),
> +					 PAGE_SIZE, __PAGE_KERNEL_RO);
> +		/*
> +		 * We do not have a good way to fail CPU bringup.
> +		 * Just WARN about it and hope we boot far enough
> +		 * to get a good log out.
> +		 */

The GDT fixmap can be set up before the CPU is started. There is no reason
to do that in cpu_init().

> +
> +	/*
> +	 * We could theoretically do this in setup_fixmap_gdt().
> +	 * But, we would need to rewrite the above page table
> +	 * allocation code to use the bootmem allocator.  The
> +	 * buddy allocator is not available at the time that we
> +	 * call setup_fixmap_gdt() for CPU 0.
> +	 */
> +	kaiser_add_user_map_early(get_cpu_gdt_ro(0), PAGE_SIZE,
> +				  __PAGE_KERNEL_RO | _PAGE_GLOBAL);

This one is needs to stay.

Thanks,

	tglx