Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759209AbXH1RX3 (ORCPT ); Tue, 28 Aug 2007 13:23:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754346AbXH1RXB (ORCPT ); Tue, 28 Aug 2007 13:23:01 -0400 Received: from ozlabs.org ([203.10.76.45]:57084 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754705AbXH1RXA (ORCPT ); Tue, 28 Aug 2007 13:23:00 -0400 Subject: [PATCH] Fix lguest page-pinning logic ("lguest: bad stack page 0xc057a000") From: Rusty Russell To: Frederik Deweerdt Cc: Andrew Morton , linux-kernel@vger.kernel.org, Linus Torvalds , lguest In-Reply-To: <20070825211405.GA18217@slug> References: <20070822020648.5ea3a612.akpm@linux-foundation.org> <20070822202551.GB31846@slug> <20070823145038.9895784f.akpm@linux-foundation.org> <20070824060438.GE31846@slug> <46CE7EDC.9080007@goop.org> <20070824082249.GG31846@slug> <1188043649.20041.81.camel@localhost.localdomain> <20070825122324.GA6138@slug> <20070825211405.GA18217@slug> Content-Type: text/plain Date: Tue, 28 Aug 2007 02:09:59 +1000 Message-Id: <1188230999.5531.15.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1617 Lines: 35 If the stack pointer is 0xc057a000, then the first stack page is at 0xc0579000 (the stack pointer is decremented before use). Not calculating this correctly caused guests with CONFIG_DEBUG_PAGEALLOC=y to be killed with a "bad stack page" message: the initial kernel stack was just preceeding the .smp_locks section which CONFIG_DEBUG_PAGEALLOC marks read-only when freeing. Thanks to Frederik Deweerdt for the bug report! Signed-off-by: Rusty Russell diff -r cb71c5b0bbb5 drivers/lguest/interrupts_and_traps.c --- a/drivers/lguest/interrupts_and_traps.c Sun Aug 26 10:31:53 2007 +1000 +++ b/drivers/lguest/interrupts_and_traps.c Sun Aug 26 10:34:44 2007 +1000 @@ -270,8 +270,11 @@ void pin_stack_pages(struct lguest *lg) /* Depending on the CONFIG_4KSTACKS option, the Guest can have one or * two pages of stack space. */ for (i = 0; i < lg->stack_pages; i++) - /* The stack grows *upwards*, hence the subtraction */ - pin_page(lg, lg->esp1 - i * PAGE_SIZE); + /* The stack grows *upwards*, so the address we're given is the + * start of the page after the kernel stack. Subtract one to + * get back onto the first stack page, and keep subtracting to + * get to the rest of the stack pages. */ + pin_page(lg, lg->esp1 - 1 - i * PAGE_SIZE); } /* Direct traps also mean that we need to know whenever the Guest wants to use - 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/