On Thu, Jun 26, 2025 at 10:50:22AM -0400, James Bottomley wrote:

On Thu, 2025-06-26 at 13:19 +0300, Jarkko Sakkinen wrote:

quoted

From: Jarkko Sakkinen <redacted>

Create a cleanup class for struct tpm_buf using DEFINE_CLASS(), which
will guarantee that the heap allocated memory will be freed
automatically for the transient instances of this structure, when
they go out of scope.

Wrap this all into help macro CLASS_TPM_BUF().

A TPM buffer can now be declared trivially:

    CLASS_TPM_BUF(buf, buf_size);

Well, that's not all ... you're also adding a size to the API that we
didn't have before, which should at least be documented in the commit
message and probably be a separate patch.

What is the reason for this, though?  The reason we currently use a
page is that it's easy for the OS to manage (no slab fragmentation
issues).  The TCG reference platform defines this to be just under 4k
(actually 4096-0x80) precisely because TPM implementations don't do
scatter gather, so they don't want it going over an ARM page, so
there's no danger of us ever needing more than a page.

Thanks for the valuable feedback.

I can drop "buf_size" parameter. It is not a priority, and I also
agree with your comments.

Regards,

James

BR, Jarkko