Re: [PATCH RFC 1/4] tpm: migrate struct tpm_buf to struct tpm_chip

[Jason Gunthorpe <jgunthorpe@obsidianresearch.com>]

On Mon, Jan 02, 2017 at 03:22:07PM +0200, Jarkko Sakkinen wrote:
> Since there is only one thread using TPM chip at a time to transmit data
> we can migrate struct tpm_buf to struct tpm_chip. This makes the use of
> it more fail safe as the buffer is allocated from heap when the device
> is created and not for every transaction.

Eh? What? I don't think that is the case..

We don't serialize until we hit tramsit_cmd at which point the buffer
is already being used and cannot be shared between threads.

Only /dev/tpmX has any sort of locking, but even that is
designed to be optional (eg I patch it out of my kernels), and only
covers userspace, not contention with in-kernel threads.

Why would the resource manager need a single global tpm buffer? That
seems like a big regression from where we have been going. I don't
think this is a good idea to go down this road.

> -	tpm_buf_append(buf, (u8 *) &value2, 4);
> +	tpm_buf_append(buf, (u8 *)&value2, 4);

Please try and avoid this sort of churn in patches that change things..

Jason