From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3r5bB56NCTzDqD8 for ; Fri, 13 May 2016 13:36:29 +1000 (AEST) Date: Fri, 13 May 2016 13:35:46 +1000 From: Paul Mackerras To: Thomas Huth Cc: Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Benjamin Herrenschmidt , kvm-ppc@vger.kernel.org, Alexander Graf , Madhavan Srinivasan Subject: Re: [PATCH] powerpc: Fix definition of SIAR and SDAR registers Message-ID: <20160513033546.GA22018@oak.ozlabs.ibm.com> References: <1463052404-18092-1-git-send-email-thuth@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1463052404-18092-1-git-send-email-thuth@redhat.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, May 12, 2016 at 01:26:44PM +0200, Thomas Huth wrote: > The SIAR and SDAR registers are available twice, one time as SPRs > 780 / 781 (unprivileged, but read-only), and one time as the SPRs > 796 / 797 (privileged, but read and write). The Linux kernel code > currently uses the unprivileged SPRs - while this is OK for reading, > writing to that register of course does not work. > Since the KVM code tries to write to this register, too (see the mtspr > in book3s_hv_rmhandlers.S), the contents of this register sometimes get > lost for the guests, e.g. during migration of a VM. > To fix this issue, simply switch to the privileged SPR numbers instead. > > Signed-off-by: Thomas Huth Acked-by: Paul Mackerras