From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 31E68280278 for ; Fri, 10 Nov 2017 04:13:43 -0500 (EST) Received: by mail-wr0-f197.google.com with SMTP id o14so4648933wrf.6 for ; Fri, 10 Nov 2017 01:13:43 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id 124sor265519wmv.23.2017.11.10.01.13.42 for (Google Transport Security); Fri, 10 Nov 2017 01:13:42 -0800 (PST) Date: Fri, 10 Nov 2017 10:13:39 +0100 From: Ingo Molnar Subject: Re: [PATCH 2/4] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time Message-ID: <20171110091339.rvqhdce55pil5c6k@gmail.com> References: <20171101115503.18358-1-kirill.shutemov@linux.intel.com> <20171101115503.18358-3-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171101115503.18358-3-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: 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 * Kirill A. Shutemov wrote: > This patch prepare decompression code to boot-time switching between 4- > and 5-level paging. > > Signed-off-by: Kirill A. Shutemov > --- > arch/x86/boot/compressed/head_64.S | 16 ++++++++++++---- > arch/x86/boot/compressed/pagetable.c | 19 +++++++++++++++++++ > 2 files changed, 31 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S > index b4a5d284391c..6ac8239af2b6 100644 > --- a/arch/x86/boot/compressed/head_64.S > +++ b/arch/x86/boot/compressed/head_64.S > @@ -288,10 +288,18 @@ ENTRY(startup_64) > leaq boot_stack_end(%rbx), %rsp > > #ifdef CONFIG_X86_5LEVEL > - /* Check if 5-level paging has already enabled */ > - movq %cr4, %rax > - testl $X86_CR4_LA57, %eax > - jnz lvl5 > + /* > + * Check if we need to enable 5-level paging. > + * RSI holds real mode data and need to be preserved across > + * a function call. > + */ > + pushq %rsi > + call need_to_enabled_l5 > + popq %rsi > + > + /* If need_to_enabled_l5() returned zero, we're done here. */ > + cmpq $0, %rax > + je lvl5 > > /* > * At this point we are in long mode with 4-level paging enabled, > diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c > index a15bbfcb3413..cd2dd49333cc 100644 > --- a/arch/x86/boot/compressed/pagetable.c > +++ b/arch/x86/boot/compressed/pagetable.c > @@ -154,3 +154,22 @@ void finalize_identity_maps(void) > } > > #endif /* CONFIG_RANDOMIZE_BASE */ > + > +#ifdef CONFIG_X86_5LEVEL > +int need_to_enabled_l5(void) > +{ > + /* Check i leaf 7 is supported. */ > + if (native_cpuid_eax(0) < 7) > + return 0; > + > + /* Check if la57 is supported. */ > + if (!(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) > + return 0; > + > + /* Check if 5-level paging has already been enabled. */ > + if (native_read_cr4() & X86_CR4_LA57) > + return 0; > + > + return 1; > +} > +#endif Ok, I like this a lot better than doing this at the assembly level - and this could provide a model for how to further reduce assembly code. Thanks, Ingo -- 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