Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755321Ab3CAUVe (ORCPT ); Fri, 1 Mar 2013 15:21:34 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51399 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752587Ab3CATpX (ORCPT ); Fri, 1 Mar 2013 14:45:23 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Darren Hart , "H. Peter Anvin" , Matt Fleming Subject: [ 26/77] x86: Make sure we can boot in the case the BDA contains pure garbage Date: Fri, 1 Mar 2013 11:44:11 -0800 Message-Id: <20130301194354.794007218@linuxfoundation.org> X-Mailer: git-send-email 1.8.1.rc1.5.g7e0651a In-Reply-To: <20130301194351.913471337@linuxfoundation.org> References: <20130301194351.913471337@linuxfoundation.org> User-Agent: quilt/0.60-2.1.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4711 Lines: 128 3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: "H. Peter Anvin" commit 7c10093692ed2e6f318387d96b829320aa0ca64c upstream. On non-BIOS platforms it is possible that the BIOS data area contains garbage instead of being zeroed or something equivalent (firmware people: we are talking of 1.5K here, so please do the sane thing.) We need on the order of 20-30K of low memory in order to boot, which may grow up to < 64K in the future. We probably want to avoid the lowest of the low memory. At the same time, it seems extremely unlikely that a legitimate EBDA would ever reach down to the 128K (which would require it to be over half a megabyte in size.) Thus, pick 128K as the cutoff for "this is insane, ignore." We may still end up reserving a bunch of extra memory on the low megabyte, but that is not really a major issue these days. In the worst case we lose 512K of RAM. This code really should be merged with trim_bios_range() in arch/x86/kernel/setup.c, but that is a bigger patch for a later merge window. Reported-by: Darren Hart Signed-off-by: H. Peter Anvin Cc: Matt Fleming Link: http://lkml.kernel.org/n/tip-oebml055yyfm8yxmria09rja@git.kernel.org Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/head.c | 57 ++++++++++++++++++++++++++++++------------------- 1 file changed, 36 insertions(+), 21 deletions(-) --- a/arch/x86/kernel/head.c +++ b/arch/x86/kernel/head.c @@ -5,8 +5,6 @@ #include #include -#define BIOS_LOWMEM_KILOBYTES 0x413 - /* * The BIOS places the EBDA/XBDA at the top of conventional * memory, and usually decreases the reported amount of @@ -16,17 +14,30 @@ * chipset: reserve a page before VGA to prevent PCI prefetch * into it (errata #56). Usually the page is reserved anyways, * unless you have no PS/2 mouse plugged in. + * + * This functions is deliberately very conservative. Losing + * memory in the bottom megabyte is rarely a problem, as long + * as we have enough memory to install the trampoline. Using + * memory that is in use by the BIOS or by some DMA device + * the BIOS didn't shut down *is* a big problem. */ + +#define BIOS_LOWMEM_KILOBYTES 0x413 +#define LOWMEM_CAP 0x9f000U /* Absolute maximum */ +#define INSANE_CUTOFF 0x20000U /* Less than this = insane */ + void __init reserve_ebda_region(void) { unsigned int lowmem, ebda_addr; - /* To determine the position of the EBDA and the */ - /* end of conventional memory, we need to look at */ - /* the BIOS data area. In a paravirtual environment */ - /* that area is absent. We'll just have to assume */ - /* that the paravirt case can handle memory setup */ - /* correctly, without our help. */ + /* + * To determine the position of the EBDA and the + * end of conventional memory, we need to look at + * the BIOS data area. In a paravirtual environment + * that area is absent. We'll just have to assume + * that the paravirt case can handle memory setup + * correctly, without our help. + */ if (paravirt_enabled()) return; @@ -37,19 +48,23 @@ void __init reserve_ebda_region(void) /* start of EBDA area */ ebda_addr = get_bios_ebda(); - /* Fixup: bios puts an EBDA in the top 64K segment */ - /* of conventional memory, but does not adjust lowmem. */ - if ((lowmem - ebda_addr) <= 0x10000) - lowmem = ebda_addr; - - /* Fixup: bios does not report an EBDA at all. */ - /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */ - if ((ebda_addr == 0) && (lowmem >= 0x9f000)) - lowmem = 0x9f000; - - /* Paranoia: should never happen, but... */ - if ((lowmem == 0) || (lowmem >= 0x100000)) - lowmem = 0x9f000; + /* + * Note: some old Dells seem to need 4k EBDA without + * reporting so, so just consider the memory above 0x9f000 + * to be off limits (bugzilla 2990). + */ + + /* If the EBDA address is below 128K, assume it is bogus */ + if (ebda_addr < INSANE_CUTOFF) + ebda_addr = LOWMEM_CAP; + + /* If lowmem is less than 128K, assume it is bogus */ + if (lowmem < INSANE_CUTOFF) + lowmem = LOWMEM_CAP; + + /* Use the lower of the lowmem and EBDA markers as the cutoff */ + lowmem = min(lowmem, ebda_addr); + lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */ /* reserve all memory between lowmem and the 1MB mark */ memblock_reserve(lowmem, 0x100000 - lowmem); -- 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/