From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id BD7F528028E for ; Fri, 10 Nov 2017 04:55:56 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id o14so4706513wrf.6 for ; Fri, 10 Nov 2017 01:55:56 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id o30sor5651812eda.56.2017.11.10.01.55.55 for (Google Transport Security); Fri, 10 Nov 2017 01:55:55 -0800 (PST) Date: Fri, 10 Nov 2017 12:55:53 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 3/4] x86/boot/compressed/64: Introduce place_trampoline() Message-ID: <20171110095553.llbcmvaakn56mhzq@node.shutemov.name> References: <20171101115503.18358-1-kirill.shutemov@linux.intel.com> <20171101115503.18358-4-kirill.shutemov@linux.intel.com> <20171110091703.7izzr7p3jkyxh7vd@gmail.com> <20171110092812.ad2i6fj5wmdmheuf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171110092812.ad2i6fj5wmdmheuf@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: "Kirill A. Shutemov" , Ingo Molnar , Linus Torvalds , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Cyrill Gorcunov , Borislav Petkov , Andi Kleen , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, Nov 10, 2017 at 10:28:12AM +0100, Ingo Molnar wrote: > > * Ingo Molnar wrote: > > > > --- a/arch/x86/boot/compressed/head_64.S > > > +++ b/arch/x86/boot/compressed/head_64.S > > > @@ -315,6 +315,18 @@ ENTRY(startup_64) > > > * The first step is go into compatibility mode. > > > */ > > > > > > + /* > > > + * Find suitable place for trampoline and populate it. > > > + * The address will be stored in RCX. > > > + * > > > + * RSI holds real mode data and need to be preserved across > > > + * a function call. > > > + */ > > > + pushq %rsi > > > + call place_trampoline > > > + popq %rsi > > > + movq %rax, %rcx > > > + > > > /* Clear additional page table */ > > > leaq lvl5_pgtable(%rbx), %rdi > > > xorq %rax, %rax > > > > One request: it's always going to be fragile if the _only_ thing that uses the > > trampoline is the 5-level paging code. > > > > Could we use the trampoline in the 4-level paging case too? It's not required, but > > would test much of the trampoline allocation and copying machinery - and the > > performance cost is negligible. > > Note that right now the trampoline is pointless on 4-level setups, so there's > nothing to copy - but we could perhaps make it meaningful. But maybe it's not a > good idea. Let me see how it will play out. > One other detail I noticed: > > /* Bound size of trampoline code */ > .org lvl5_trampoline_src + LVL5_TRAMPOLINE_CODE_SIZE > > will this generate a build error if the trampoline code exceeds 0x40? Yes, this is the point. Just a failsafe if trampoline code would grew too much. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org