Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752531Ab1EIPjG (ORCPT ); Mon, 9 May 2011 11:39:06 -0400 Received: from service87.mimecast.com ([94.185.240.25]:51289 "HELO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751219Ab1EIPjE convert rfc822-to-8bit (ORCPT ); Mon, 9 May 2011 11:39:04 -0400 Subject: Re: [PATCH v5 02/19] ARM: LPAE: add ISBs around MMU enabling code From: Catalin Marinas To: Russell King - ARM Linux Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Will Deacon In-Reply-To: <20110509153416.GC16919@n2100.arm.linux.org.uk> References: <1304859098-10760-1-git-send-email-catalin.marinas@arm.com> <1304859098-10760-3-git-send-email-catalin.marinas@arm.com> <20110508214101.GO27807@n2100.arm.linux.org.uk> <1304936539.7658.31.camel@e102109-lin.cambridge.arm.com> <20110509103242.GQ27807@n2100.arm.linux.org.uk> <1304938794.7658.56.camel@e102109-lin.cambridge.arm.com> <20110509120509.GR27807@n2100.arm.linux.org.uk> <1304953316.7658.71.camel@e102109-lin.cambridge.arm.com> <20110509153416.GC16919@n2100.arm.linux.org.uk> Organization: ARM Limited Date: Mon, 09 May 2011 16:38:50 +0100 Message-ID: <1304955530.7658.74.camel@e102109-lin.cambridge.arm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 X-OriginalArrivalTime: 09 May 2011 15:39:00.0324 (UTC) FILETIME=[3787F240:01CC0E5F] X-MC-Unique: 111050916390105201 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1885 Lines: 48 On Mon, 2011-05-09 at 16:34 +0100, Russell King - ARM Linux wrote: > On Mon, May 09, 2011 at 04:01:56PM +0100, Catalin Marinas wrote: > > This doesn't work. From the ARM ARM (B1.3.3): > > > > The execution state bits are the IT[7:0], J, E, and T bits. In > > exception modes you can read or write these bits in the current > > SPSR. > > In the CPSR, unless the processor is in Debug state: > > • The execution state bits, other than the E bit, are RAZ when > > read by an MRS instruction. > > > > So reading the CPSR doesn't copy the T and E bits. Of course, we could > > set them explicitly but I find the ISB much simpler (and in practice we > > only need it for ARMv7 onwards but adding the ARMv6 in case we have a > > kernel compiled for both). > > Err. If that's correct then the Linux kernel is totally broken, and > that's an incompatible change to the behaviour of the MRS and MSR > instructions which has gone unnoticed. > > We use "MRS reg, cpsr" for saving the IRQ state in SVC mode and > "MSR cpsr, reg" to restore the interrupt state. If the T bit gets > reset by that, then Thumb kernels can never work. > > What you've just said tells me that our implementation of: > - arch_local_irq_save() > - arch_local_save_flags() > - arch_local_irq_restore() > won't work because we can't read or write the I and F bits using > MSR/MRS, even in SVC mode. You can't write the execution state bits: IT[7:0], E and T. You can write mask bits A, I and F using MSR. > What is the replacement method for doing this? For changing the execution state - SETEND, BX etc. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/