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From: Alexander Kuleshov <kuleshovmail@gmail.com>
To: Brian Gerst <brgerst@gmail.com>
Cc: Alexander Kuleshov <kuleshovmail@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
Date: Sat, 23 Jan 2016 12:37:56 +0600	[thread overview]
Message-ID: <20160123063756.GB1205@localhost> (raw)
In-Reply-To: <CAMzpN2gR2dpyDU1RDKtq0oeOqcFuJiVtMkN9TkZSUGQrsjGEJQ@mail.gmail.com>

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.

      reply	other threads:[~2016-01-23  6:41 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-22 18:13 [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned Alexander Kuleshov
2016-01-23  1:42 ` Brian Gerst
2016-01-23  6:37   ` Alexander Kuleshov [this message]

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