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SubjectRe: [patch 2/5] x86/idt: Add comments about early #PF handling
On Thu, May 28, 2020 at 04:53:17PM +0200, Thomas Gleixner wrote:
> The difference between 32 and 64 bit vs. early #PF handling is not
> documented. Replace the FIXME at idt_setup_early_pf() with proper comments.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/kernel/idt.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -61,7 +61,11 @@ static bool idt_setup_done __initdata;
> static const __initconst struct idt_data early_idts[] = {
> INTG(X86_TRAP_DB, asm_exc_debug),
> SYSG(X86_TRAP_BP, asm_exc_int3),
> +
> #ifdef CONFIG_X86_32
> + /*
> + * Not possible on 64-bit. See idt_setup_early_pf() for details.
> + */
> INTG(X86_TRAP_PF, asm_exc_page_fault),
> #endif
> };
> @@ -276,8 +280,10 @@ void __init idt_setup_traps(void)
> * cpu_init() is invoked and sets up TSS. The IST variant is installed
> * after that.
> *
> - * FIXME: Why is 32bit and 64bit installing the PF handler at different
> - * places in the early setup code?
> + * Note, that X86_64 cannot install the real #PF handler in
> + * idt_setup_early_traps() because the memory intialization needs the #PF
> + * handler from the early_idt_handler_array to initialize the early page
> + * tables.

+ "See early_make_pgtables()" ?

I had to frob around in head_64.S to find wth that early handler
actually did.

> */
> void __init idt_setup_early_pf(void)
> {
>

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