linux-kernel - Re: [PATCH v2 2/3] platform/x86/intel/tpmi: Add debugfs interface

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Message-ID: <ZK7DNdlUvUZ5deho@smile.fi.intel.com>
Date:   Wed, 12 Jul 2023 18:13:57 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     hdegoede@...hat.com, markgross@...nel.org,
        ilpo.jarvinen@...ux.intel.com, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] platform/x86/intel/tpmi: Add debugfs interface

On Tue, Jul 11, 2023 at 03:09:48PM -0700, Srinivas Pandruvada wrote:
> Add debugfs interface for debugging TPMI configuration and register
> contents. This shows PFS (PM Feature structure) for each TPMI device.
> 
> For each feature, show full register contents and allow to modify
> register at an offset.
> 
> This debugfs interface is not present on locked down kernel with no
> DEVMEM access and without CAP_SYS_RAWIO permission.

...

>  struct intel_tpmi_pm_feature {
>  	struct intel_tpmi_pfs_entry pfs_header;
>  	unsigned int vsec_offset;
> +	struct intel_vsec_device *vsec_dev;

Hmm... I don't know the layout of pfs_header, but this may be 4 bytes less
if you move it upper.

>  };

...

> +	for (count = 0; count < pfs->pfs_header.num_entries; ++count) {

> +		size = pfs->pfs_header.entry_size * sizeof(u32);

You already used this once, perhaps a macro helper?
Also you can add there a comment that this comes from the trusted hw.

> +		/* The size is from a trusted hardware, but verify anyway */
> +		if (size > TPMI_MAX_BUFFER_SIZE) {
> +			/*
> +			 * The next offset depends on the current size. So, can't skip to the
> +			 * display of the next entry. Simply return from this function with error.
> +			 */
> +			ret = -EIO;
> +			goto done_mem_show;
> +		}
> +
> +		buffer = kmalloc(size, GFP_KERNEL);
> +		if (!buffer) {
> +			ret = -ENOMEM;
> +			goto done_mem_show;
> +		}
> +
> +		seq_printf(s, "TPMI Instance:%d offset:0x%x\n", count, off);
> +
> +		mem = ioremap(off, size);
> +		if (!mem) {
> +			ret = -ENOMEM;
> +			kfree(buffer);
> +			goto done_mem_show;
> +		}
> +
> +		memcpy_fromio(buffer, mem, size);
> +
> +		seq_hex_dump(s, " ", DUMP_PREFIX_OFFSET, row_size, sizeof(u32), buffer, size,
> +			     false);
> +
> +		iounmap(mem);
> +		kfree(buffer);
> +
> +		off += size;
> +	}
> +
> +done_mem_show:
> +	mutex_unlock(&tpmi_dev_lock);
> +
> +	return ret;
> +}

...

> +	size = pfs->pfs_header.entry_size * sizeof(u32);
> +	if (size > TPMI_MAX_BUFFER_SIZE)
> +		return -EIO;

Again a dup even with a check.

...

> +	top_dir = debugfs_create_dir(name, NULL);
> +	if (IS_ERR_OR_NULL(top_dir))

I dunno if I told you, but after a discussion (elsewhere), I realized
two things:
1) this one never returns NULL;
2) even if error pointer is returned, the debugfs API is aware and
   will do nothing.

Hence this conditional is redundant.

> +		return;

...

> +	for (i = 0; i < tpmi_info->feature_count; ++i) {

Why preincrement?

> +		struct intel_tpmi_pm_feature *pfs;
> +		struct dentry *dir;
> +
> +		pfs = &tpmi_info->tpmi_features[i];
> +		snprintf(name, sizeof(name), "tpmi-id-%02x", pfs->pfs_header.tpmi_id);
> +		dir = debugfs_create_dir(name, top_dir);
> +
> +		debugfs_create_file("mem_dump", 0444, dir, pfs, &tpmi_mem_dump_fops);
> +		debugfs_create_file("mem_write", 0644, dir, pfs, &mem_write_ops);
> +	}

-- 
With Best Regards,
Andy Shevchenko