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SubjectRe: [PATCH 12/30] x86, kaiser: map GDT into user page tables
On Mon, Nov 20, 2017 at 12:22 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> 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.

When you rebase on to my latest version, this should change to mapping
the entire cpu_entry_area.

--Andy

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