Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned

[Alexander Kuleshov]

Hello Brian,

On 01-22-16, Brian Gerst wrote:
> >
> > -       /* Is the address not 2M aligned? */
> > -       movq    %rbp, %rax
> > -       andl    $~PMD_PAGE_MASK, %eax
> > -       testl   %eax, %eax
> > -       jnz     bad_address
> > -
> >         /*
> >          * Is the address too large?
> >          */
> 
> I think we still need to do the check, in case we came from a 64-bit
> bootloader that directly jumped to startup_64.  However, this check
> can be simplified to:
> 
>     testl $~PMD_PAGE_MASK, %ebp
>     jnz bad_address

Ah, ok, in this way we can't trust a bootloader. I just thought that
64-bit entry point is startup_64 from arch/x86/boot/compressed/head_64.S

Thank you.