Re: [PATCH v14 9/9] RFC: fw_cfg: do DMA read operation

From: Michael S. Tsirkin
Date: Wed Feb 14 2018 - 12:00:06 EST


On Wed, Feb 14, 2018 at 05:52:10PM +0100, Marc-Andre Lureau wrote:
> >> @@ -282,8 +320,9 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
> >> #endif
> >>
> >> /* verify fw_cfg device signature */
> >> - fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
> >> - if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
> >> + if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig,
> >> + 0, FW_CFG_SIG_SIZE, false) < 0 ||
> >> + memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
> >> fw_cfg_io_cleanup();
> >> return -ENODEV;
> >> }
> >
> > Rather than add dead code, how about a promise not to
> > fail if dma is disabled? Patch will be smaller then.
>
> Even with dma disabled, you could have a locking bug which was
> silently ignored before and is now taken into account.

I see. I'd start with a patch reporting errors to users then.
That would be a bugfix and can be merged for this version.

> >
> >> @@ -466,8 +505,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> >> if (count > entry->size - pos)
> >> count = entry->size - pos;
> >>
> >> - fw_cfg_read_blob(entry->select, buf, pos, count);
> >> - return count;
> >> + /* do not use DMA, virt_to_phys(buf) might not be ok */
> >> + return fw_cfg_read_blob(entry->select, buf, pos, count, false);
> >> }
> >>
> >> static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> >> @@ -632,7 +671,12 @@ static int fw_cfg_register_dir_entries(void)
> >> struct fw_cfg_file *dir;
> >> size_t dir_size;
> >>
> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count, 0, sizeof(files.count));
> >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count,
> >> + 0, sizeof(files.count), false);
> >> + if (ret < 0) {
> >> + return ret;
> >> + }
> >> +
> >> count = be32_to_cpu(files.count);
> >> dir_size = count * sizeof(struct fw_cfg_file);
> >>
> >> @@ -640,7 +684,11 @@ static int fw_cfg_register_dir_entries(void)
> >> if (!dir)
> >> return -ENOMEM;
> >>
> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(files.count), dir_size);
> >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir,
> >> + sizeof(files.count), dir_size, false);
> >> + if (ret < 0) {
> >> + goto end;
> >> + }
> >>
> >> for (i = 0; i < count; i++) {
> >> ret = fw_cfg_register_file(&dir[i]);
> >> @@ -648,6 +696,7 @@ static int fw_cfg_register_dir_entries(void)
> >> break;
> >> }
> >>
> >> +end:
> >> kfree(dir);
> >> return ret;
> >> }
> >> @@ -688,7 +737,10 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
> >> goto err_probe;
> >>
> >> /* get revision number, add matching top-level attribute */
> >> - fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
> >> + err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), false);
> >> + if (err < 0) {
> >> + goto err_probe;
> >> + }
> >> fw_cfg_rev = le32_to_cpu(rev);
> >> err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
> >> if (err)
> >> --
> >> 2.16.1.73.g5832b7e9f2