From mboxrd@z Thu Jan 1 00:00:00 1970 From: kanoj@google.engr.sgi.com (Kanoj Sarcar) Message-Id: <199908162328.QAA24338@google.engr.sgi.com> Subject: Re: [bigmem-patch] 4GB with Linux on IA32 Date: Mon, 16 Aug 1999 16:28:58 -0700 (PDT) In-Reply-To: from "Andrea Arcangeli" at Aug 16, 99 10:54:45 pm MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: alan@lxorguk.ukuu.org.uk, torvalds@transmeta.com, sct@redhat.com, Gerhard.Wichert@pdb.siemens.de, Winfried.Gerhard@pdb.siemens.de, linux-kernel@vger.rutgers.edu, linux-mm@kvack.org List-ID: > > On Mon, 16 Aug 1999, Alan Cox wrote: > > >> a range of user pages that were in bigmem area? Also, debuggers > >> want to look at user memory, so they would also need to map the > >> pages. Are there any other cases where a driver might want to > > > >That is the tricky one. What occurs if I mmap a high memory page of > >another process via /proc/pid/mem ? then write it > > IMO Kanoj was talking about another thing (ptrace). > Andrea, I was also talking about drivers which assume that all of memory is direct mapped. For example, __va and __pa assume this. There might be other macros/procedures which have the same assumption built in. Basically, anything that is dependent on PAGE_OFFSET needs to be checked. For example, on a 2.2.10 kernel: [kanoj@entity kern]$ gid __va | grep drivers drivers/char/mem.c:124: if (copy_to_user(buf, __va(p), count)) drivers/char/mem.c:142: return do_write_mem(file, __va(p), p, buf, count, ppos); drivers/scsi/sym53c8xx.c:572:#define remap_pci_mem(base, size) ((u_long) __va(base)) drivers/video/creatorfb.c:684: disp->screen_base = (char *)__va(regs[0].phys_addr) + FFB_DFB24_POFF + 8192 * fb->y_margin + 4 * fb->x_margin; drivers/video/creatorfb.c:687: fb->s.ffb.fbc = (struct ffb_fbc *)((char *)__va(regs[0].phys_addr) + FFB_FBC_REGS_POFF); drivers/video/creatorfb.c:688: fb->s.ffb.dac = (struct ffb_dac *)((char *)__va(regs[0].phys_addr) + FFB_DAC_POFF); drivers/sbus/char/zs.c:1934: __va((((unsigned long)zsregs[0].which_io)<<32) | For all such macros, a decision needs to be made whether such usage will create problems if the underlying page happens to be a bigmem page. If so, the proper mapping (and unmapping) calls need to be made around the kernel code that accesses the page contents. Kanoj -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/