From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 6 Jun 2001 17:14:26 -0400 From: cohutta Subject: RE: temp. mem mappings Message-ID: <3B2C3149@MailAndNews.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Stephen C. Tweedie" Cc: linux-mm List-ID: >===== Original Message From "Stephen C. Tweedie" ===== >Hi, > >On Tue, Jun 05, 2001 at 04:42:52PM -0400, cohutta wrote: > >> I don't really want to play with the page tables if i can help it. >> I didn't use ioremap() because it's real system memory, not IO bus >> memory. >> >> How much normal memory is identity-mapped at boot on x86? >> Is it more than 8 MB? > >> I'm trying to read some ACPI tables, like the FACP. >> On my system, this is at physical address 0x3fffd7d7 (e.g.). > >It depends at what time during boot. Some ACPI memory is reusable >once the system boots: the kernel parses the table then frees up the >memory which the BIOS initialised. > >VERY early in boot, while the VM is still getting itself set up, there >is only a minimal mapping set up by the boot loader code. However, >once the VM is initialised far enough to let you play with page >tables, all memory will be identity-mapped up to just below the 1GB >watermark. I think this is part of the problem: on my 1 GB system, the ACPI tables are at physical 0x3fffxxxx == virtual 0xffffxxxx, which could conflict with the APIC and IOAPIC mappings (from fixmap.h). I removed 256 MB, but i still have a few problems. >> kmap() ends up calling set_pte(), which is close to what i am >> already doing. i'm having a problem on the unmap side when i >> am done with the temporary mapping. > >kunmap(). :-) But kmap only works on CONFIG_HIGHMEM kernel builds. >On kernels built without high memory support, kmap will not allow you >to access memory beyond the normal physical memory boundary. Well, i'm talking about physical memory, but it's marked as ACPI data. Another part of the problem is that I need to do this early in arch/i386/kernel/setup.c::setup_arch(), like between calls to paging_init() and init_apic_mappings(). I can't use ioremap() here can i? ioremap() calls get_vm_area() which calls kmalloc(), and i don't think i can use kmalloc() just yet. methinks that i'm back to a modification of Timur's suggestion-- a bunch of manual page dir/table changes. Any other suggestions or corrections to my comments? thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/