From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Re: [PATCH] SeaBIOS/Xen: Compute the low RAM memory size in the BDA according to the e820 Date: Mon, 14 Nov 2011 08:53:53 +0000 Message-ID: References: <20111114033618.GA30104@morn.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111114033618.GA30104@morn.localdomain> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Kevin O'Connor , Julian Pidancet Cc: xen-devel@lists.xensource.com, seabios@seabios.org, ian.campbell@citrix.com List-Id: xen-devel@lists.xenproject.org On 14/11/2011 03:36, "Kevin O'Connor" wrote: >> Like I said, I'm not an ACPI expert. But let say we decide to move >> this ACPI info structure to some other area, where there's less risk >> for it to be overwritten, like somewhere above 0xFC000000, wouldn't >> that prevent some Operating System with limited memory capabilities to >> access it ? > > If the OS can handle AML it can handle 32bit addresses. > >> Besides, it seems that SeaBIOS manages itself the space between >> 0xFC000000 and 4G, so it seems difficult to imagine to have a reserved >> space with a fixed address in there. > > On Xen, the PCI init code isn't used, so assuming this struct doesn't > need to live in real "ram", I think it could live just about anywhere > past the end of ram. Even with pciinit.c, addresses over 0xfc00000 > (with the exception of a few bytes for hpet, apic, ioapic, and bios > image) could be used. I suggest we stick it at FC000000, and shift hvmloader's mem_alloc() starting address up by one page to FC001000. The acpi build code will have to manually mem_hole_populate_ram() that one page before writing to it. This can then be documented in hvmloader/config.h which contains a description of, and defines for, the system memory map. This is by far the easiest solution to this problem; manually crafting an SSDT is a right pain in the arse, whereas this is maybe a 5-line patch. -- Keir > -Kevin > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel