From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id 90F4A440D41 for ; Fri, 10 Nov 2017 17:04:09 -0500 (EST) Received: by mail-pg0-f71.google.com with SMTP id m188so476812pga.22 for ; Fri, 10 Nov 2017 14:04:09 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id g17si8545305plo.542.2017.11.10.14.04.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 10 Nov 2017 14:04:08 -0800 (PST) Received: from mail-io0-f175.google.com (mail-io0-f175.google.com [209.85.223.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A8A3C218E3 for ; Fri, 10 Nov 2017 22:04:07 +0000 (UTC) Received: by mail-io0-f175.google.com with SMTP id f20so15031479ioj.9 for ; Fri, 10 Nov 2017 14:04:07 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171110193146.5908BE13@viggo.jf.intel.com> References: <20171110193058.BECA7D88@viggo.jf.intel.com> <20171110193146.5908BE13@viggo.jf.intel.com> From: Andy Lutomirski Date: Fri, 10 Nov 2017 14:03:46 -0800 Message-ID: Subject: Re: [PATCH 21/30] x86, mm: put mmu-to-h/w ASID translation in one place Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , moritz.lipp@iaik.tugraz.at, Daniel Gruss , michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, Andrew Lutomirski , Linus Torvalds , Kees Cook , Hugh Dickins , X86 ML On Fri, Nov 10, 2017 at 11:31 AM, Dave Hansen wrote: > > From: Dave Hansen > > There are effectively two ASID types: > 1. The one stored in the mmu_context that goes from 0->5 > 2. The one programmed into the hardware that goes from 1->6 > > This consolidates the locations where converting beween the two > (by doing +1) to a single place which gives us a nice place to > comment. KAISER will also need to, given an ASID, know which > hardware ASID to flush for the userspace mapping. > > Signed-off-by: Dave Hansen > Cc: Moritz Lipp > Cc: Daniel Gruss > Cc: Michael Schwarz > Cc: Richard Fellner > Cc: Andy Lutomirski > Cc: Linus Torvalds > Cc: Kees Cook > Cc: Hugh Dickins > Cc: x86@kernel.org > --- > > b/arch/x86/include/asm/tlbflush.h | 30 ++++++++++++++++++------------ > 1 file changed, 18 insertions(+), 12 deletions(-) > > diff -puN arch/x86/include/asm/tlbflush.h~kaiser-pcid-pre-build-kern arch/x86/include/asm/tlbflush.h > --- a/arch/x86/include/asm/tlbflush.h~kaiser-pcid-pre-build-kern 2017-11-10 11:22:16.521244931 -0800 > +++ b/arch/x86/include/asm/tlbflush.h 2017-11-10 11:22:16.525244931 -0800 > @@ -87,21 +87,26 @@ static inline u64 inc_mm_tlb_gen(struct > */ > #define MAX_ASID_AVAILABLE ((1< > -/* > - * If PCID is on, ASID-aware code paths put the ASID+1 into the PCID > - * bits. This serves two purposes. It prevents a nasty situation in > - * which PCID-unaware code saves CR3, loads some other value (with PCID > - * == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if > - * the saved ASID was nonzero. It also means that any bugs involving > - * loading a PCID-enabled CR3 with CR4.PCIDE off will trigger > - * deterministically. > - */ > +static inline u16 kern_asid(u16 asid) > +{ > + VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE); > + /* > + * If PCID is on, ASID-aware code paths put the ASID+1 into the PCID > + * bits. This serves two purposes. It prevents a nasty situation in > + * which PCID-unaware code saves CR3, loads some other value (with PCID > + * == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if > + * the saved ASID was nonzero. It also means that any bugs involving > + * loading a PCID-enabled CR3 with CR4.PCIDE off will trigger > + * deterministically. > + */ > + return asid + 1; > +} This seems really error-prone. Maybe we should have a pcid_t type and make all the interfaces that want a h/w PCID take pcid_t. --Andy -- 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