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 ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3v8frs39zDzDq60 for ; Fri, 27 Jan 2017 11:33:01 +1100 (AEDT) In-Reply-To: <20170119031910.2335-1-anton@ozlabs.org> To: Anton Blanchard , benh@kernel.crashing.org, paulus@samba.org, mikey@neuling.org, maddy@linux.vnet.ibm.com, grimm@linux.vnet.ibm.com From: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Subject: Re: powerpc: Ignore reserved field in DCSR and PVR reads and writes Message-Id: <3v8frs23GNz9t1Q@ozlabs.org> Date: Fri, 27 Jan 2017 11:33:01 +1100 (AEDT) List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2017-01-19 at 03:19:10 UTC, Anton Blanchard wrote: > From: Anton Blanchard > > IBM bit 31 (for the rest of us - bit 0) is a reserved field in the > instruction definition of mtspr and mfspr. Hardware is encouraged to > (and does) ignore it. > > As a result, if userspace executes an mtspr DSCR with the reserved bit > set, we get a DSCR facility unavailable exception. The kernel fails to > match against the expected value/mask, and we silently return to > userspace to try and re-execute the same mtspr DSCR instruction. We > loop forever until the process is killed. > > We should do something here, and it seems mirroring what hardware does > is the better option vs killing the process. While here, relax the > matching of mfspr PVR too. > > Signed-off-by: Anton Blanchard Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/178f358208ceb8b38e5cff3f815e0d cheers