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

From	Alexander Kuleshov <kuleshovmail@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
Date	2016-01-23 07:50 +0100
Message-ID	<qU0bf-7h2-3@gated-at.bofh.it> (permalink)
References	<qTOtr-7NF-13@gated-at.bofh.it> <qTVuV-3XO-1@gated-at.bofh.it>
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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.

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[RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned Alexander Kuleshov <kuleshovmail@gmail.com> - 2016-01-22 19:20 +0100
  Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel  address is 2M aligned Brian Gerst <brgerst@gmail.com> - 2016-01-23 02:50 +0100
    Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel  address is 2M aligned Alexander Kuleshov <kuleshovmail@gmail.com> - 2016-01-23 07:50 +0100

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