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[IA64] update memory attribute aliasing documentation & test cases
Updates documentation and adds some test cases. Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Bjorn Helgaas
Tony Luck
parent
6d40fc514c
commit
ddd83eff58
247
Documentation/ia64/aliasing-test.c
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247
Documentation/ia64/aliasing-test.c
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@ -0,0 +1,247 @@
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/*
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* Exercise /dev/mem mmap cases that have been troublesome in the past
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*
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* (c) Copyright 2007 Hewlett-Packard Development Company, L.P.
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* Bjorn Helgaas <bjorn.helgaas@hp.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <dirent.h>
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#include <fcntl.h>
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#include <fnmatch.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <unistd.h>
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int sum;
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int map_mem(char *path, off_t offset, size_t length, int touch)
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{
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int fd, rc;
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void *addr;
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int *c;
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fd = open(path, O_RDWR);
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if (fd == -1) {
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perror(path);
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return -1;
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}
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addr = mmap(NULL, length, PROT_READ|PROT_WRITE, MAP_SHARED, fd, offset);
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if (addr == MAP_FAILED)
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return 1;
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if (touch) {
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c = (int *) addr;
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while (c < (int *) (offset + length))
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sum += *c++;
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}
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rc = munmap(addr, length);
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if (rc == -1) {
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perror("munmap");
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return -1;
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}
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close(fd);
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return 0;
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}
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int scan_sysfs(char *path, char *file, off_t offset, size_t length, int touch)
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{
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struct dirent **namelist;
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char *name, *path2;
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int i, n, r, rc, result = 0;
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struct stat buf;
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n = scandir(path, &namelist, 0, alphasort);
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if (n < 0) {
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perror("scandir");
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return -1;
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}
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for (i = 0; i < n; i++) {
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name = namelist[i]->d_name;
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if (fnmatch(".", name, 0) == 0)
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goto skip;
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if (fnmatch("..", name, 0) == 0)
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goto skip;
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path2 = malloc(strlen(path) + strlen(name) + 3);
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strcpy(path2, path);
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strcat(path2, "/");
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strcat(path2, name);
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if (fnmatch(file, name, 0) == 0) {
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rc = map_mem(path2, offset, length, touch);
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if (rc == 0)
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fprintf(stderr, "PASS: %s 0x%lx-0x%lx is %s\n", path2, offset, offset + length, touch ? "readable" : "mappable");
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else if (rc > 0)
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fprintf(stderr, "PASS: %s 0x%lx-0x%lx not mappable\n", path2, offset, offset + length);
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else {
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fprintf(stderr, "FAIL: %s 0x%lx-0x%lx not accessible\n", path2, offset, offset + length);
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return rc;
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}
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} else {
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r = lstat(path2, &buf);
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if (r == 0 && S_ISDIR(buf.st_mode)) {
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rc = scan_sysfs(path2, file, offset, length, touch);
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if (rc < 0)
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return rc;
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}
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}
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result |= rc;
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free(path2);
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skip:
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free(namelist[i]);
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}
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free(namelist);
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return rc;
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}
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char buf[1024];
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int read_rom(char *path)
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{
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int fd, rc;
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size_t size = 0;
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fd = open(path, O_RDWR);
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if (fd == -1) {
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perror(path);
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return -1;
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}
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rc = write(fd, "1", 2);
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if (rc <= 0) {
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perror("write");
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return -1;
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}
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do {
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rc = read(fd, buf, sizeof(buf));
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if (rc > 0)
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size += rc;
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} while (rc > 0);
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close(fd);
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return size;
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}
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int scan_rom(char *path, char *file)
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{
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struct dirent **namelist;
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char *name, *path2;
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int i, n, r, rc, result = 0;
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struct stat buf;
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n = scandir(path, &namelist, 0, alphasort);
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if (n < 0) {
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perror("scandir");
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return -1;
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}
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for (i = 0; i < n; i++) {
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name = namelist[i]->d_name;
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if (fnmatch(".", name, 0) == 0)
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goto skip;
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if (fnmatch("..", name, 0) == 0)
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goto skip;
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path2 = malloc(strlen(path) + strlen(name) + 3);
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strcpy(path2, path);
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strcat(path2, "/");
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strcat(path2, name);
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if (fnmatch(file, name, 0) == 0) {
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rc = read_rom(path2);
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/*
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* It's OK if the ROM is unreadable. Maybe there
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* is no ROM, or some other error ocurred. The
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* important thing is that no MCA happened.
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*/
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if (rc > 0)
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fprintf(stderr, "PASS: %s read %ld bytes\n", path2, rc);
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else {
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fprintf(stderr, "PASS: %s not readable\n", path2);
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return rc;
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}
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} else {
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r = lstat(path2, &buf);
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if (r == 0 && S_ISDIR(buf.st_mode)) {
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rc = scan_rom(path2, file);
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if (rc < 0)
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return rc;
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}
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}
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result |= rc;
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free(path2);
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skip:
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free(namelist[i]);
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}
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free(namelist);
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return rc;
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}
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main()
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{
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int rc;
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if (map_mem("/dev/mem", 0, 0xA0000, 1) == 0)
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fprintf(stderr, "PASS: /dev/mem 0x0-0xa0000 is readable\n");
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else
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fprintf(stderr, "FAIL: /dev/mem 0x0-0xa0000 not accessible\n");
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/*
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* It's not safe to blindly read the VGA frame buffer. If you know
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* how to poke the card the right way, it should respond, but it's
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* not safe in general. Many machines, e.g., Intel chipsets, cover
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* up a non-responding card by just returning -1, but others will
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* report the failure as a machine check.
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*/
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if (map_mem("/dev/mem", 0xA0000, 0x20000, 0) == 0)
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fprintf(stderr, "PASS: /dev/mem 0xa0000-0xc0000 is mappable\n");
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else
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fprintf(stderr, "FAIL: /dev/mem 0xa0000-0xc0000 not accessible\n");
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if (map_mem("/dev/mem", 0xC0000, 0x40000, 1) == 0)
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fprintf(stderr, "PASS: /dev/mem 0xc0000-0x100000 is readable\n");
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else
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fprintf(stderr, "FAIL: /dev/mem 0xc0000-0x100000 not accessible\n");
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/*
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* Often you can map all the individual pieces above (0-0xA0000,
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* 0xA0000-0xC0000, and 0xC0000-0x100000), but can't map the whole
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* thing at once. This is because the individual pieces use different
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* attributes, and there's no single attribute supported over the
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* whole region.
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*/
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rc = map_mem("/dev/mem", 0, 1024*1024, 0);
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if (rc == 0)
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fprintf(stderr, "PASS: /dev/mem 0x0-0x100000 is mappable\n");
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else if (rc > 0)
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fprintf(stderr, "PASS: /dev/mem 0x0-0x100000 not mappable\n");
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else
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fprintf(stderr, "FAIL: /dev/mem 0x0-0x100000 not accessible\n");
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scan_sysfs("/sys/class/pci_bus", "legacy_mem", 0, 0xA0000, 1);
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scan_sysfs("/sys/class/pci_bus", "legacy_mem", 0xA0000, 0x20000, 0);
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scan_sysfs("/sys/class/pci_bus", "legacy_mem", 0xC0000, 0x40000, 1);
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scan_sysfs("/sys/class/pci_bus", "legacy_mem", 0, 1024*1024, 0);
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scan_rom("/sys/devices", "rom");
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}
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@ -112,16 +112,6 @@ POTENTIAL ATTRIBUTE ALIASING CASES
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The /dev/mem mmap constraints apply.
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However, since this is for mapping legacy MMIO space, WB access
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does not make sense. This matters on machines without legacy
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VGA support: these machines may have WB memory for the entire
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first megabyte (or even the entire first granule).
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On these machines, we could mmap legacy_mem as WB, which would
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be safe in terms of attribute aliasing, but X has no way of
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knowing that it is accessing regular memory, not a frame buffer,
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so the kernel should fail the mmap rather than doing it with WB.
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read/write of /dev/mem
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This uses copy_from_user(), which implicitly uses a kernel
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@ -138,14 +128,20 @@ POTENTIAL ATTRIBUTE ALIASING CASES
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ioremap()
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This returns a kernel identity mapping for use inside the
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kernel.
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This returns a mapping for use inside the kernel.
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If the region is in kern_memmap, we should use the attribute
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specified there. Otherwise, if the EFI memory map reports that
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the entire granule supports WB, we should use that (granules
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that are partially reserved or occupied by firmware do not appear
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in kern_memmap). Otherwise, we should use a UC mapping.
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specified there.
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If the EFI memory map reports that the entire granule supports
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WB, we should use that (granules that are partially reserved
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or occupied by firmware do not appear in kern_memmap).
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If the granule contains non-WB memory, but we can cover the
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region safely with kernel page table mappings, we can use
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ioremap_page_range() as most other architectures do.
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Failing all of the above, we have to fall back to a UC mapping.
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PAST PROBLEM CASES
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@ -158,7 +154,7 @@ PAST PROBLEM CASES
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succeed. It may create either WB or UC user mappings, depending
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on whether the region is in kern_memmap or the EFI memory map.
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mmap of 0x0-0xA0000 /dev/mem by "hwinfo" on HP sx1000 with VGA enabled
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mmap of 0x0-0x9FFFF /dev/mem by "hwinfo" on HP sx1000 with VGA enabled
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See https://bugzilla.novell.com/show_bug.cgi?id=140858.
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@ -171,28 +167,25 @@ PAST PROBLEM CASES
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so it is safe to use WB mappings.
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The kernel VGA driver may ioremap the VGA frame buffer at 0xA0000,
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which will use a granule-sized UC mapping covering 0-0xFFFFF. This
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granule covers some WB-only memory, but since UC is non-speculative,
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the processor will never generate an uncacheable reference to the
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WB-only areas unless the driver explicitly touches them.
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which uses a granule-sized UC mapping. This granule will cover some
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WB-only memory, but since UC is non-speculative, the processor will
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never generate an uncacheable reference to the WB-only areas unless
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the driver explicitly touches them.
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mmap of 0x0-0xFFFFF legacy_mem by "X"
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If the EFI memory map reports this entire range as WB, there
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is no VGA MMIO hole, and the mmap should fail or be done with
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a WB mapping.
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If the EFI memory map reports that the entire range supports the
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same attributes, we can allow the mmap (and we will prefer WB if
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supported, as is the case with HP sx[12]000 machines with VGA
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disabled).
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There's no easy way for X to determine whether the 0xA0000-0xBFFFF
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region is a frame buffer or just memory, so I think it's best to
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just fail this mmap request rather than using a WB mapping. As
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far as I know, there's no need to map legacy_mem with WB
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mappings.
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If EFI reports the range as partly WB and partly UC (as on sx[12]000
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machines with VGA enabled), we must fail the mmap because there's no
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safe attribute to use.
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Otherwise, a UC mapping of the entire region is probably safe.
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The VGA hole means the region will not be in kern_memmap. The
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HP sx1000 chipset doesn't support UC access to the memory surrounding
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the VGA hole, but X doesn't need that area anyway and should not
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reference it.
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If EFI reports some of the range but not all (as on Intel firmware
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that doesn't report the VGA frame buffer at all), we should fail the
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mmap and force the user to map just the specific region of interest.
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mmap of 0xA0000-0xBFFFF legacy_mem by "X" on HP sx1000 with VGA disabled
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@ -202,6 +195,16 @@ PAST PROBLEM CASES
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This is a special case of the previous case, and the mmap should
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fail for the same reason as above.
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read of /sys/devices/.../rom
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For VGA devices, this may cause an ioremap() of 0xC0000. This
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used to be done with a UC mapping, because the VGA frame buffer
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at 0xA0000 prevents use of a WB granule. The UC mapping causes
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an MCA on HP sx[12]000 chipsets.
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We should use WB page table mappings to avoid covering the VGA
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frame buffer.
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NOTES
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[1] SDM rev 2.2, vol 2, sec 4.4.1.
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