linux-kernel - Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class

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Message-ID: <jkr5z4thb55gs2jcmtcfipgg6p7z6ikhr6etd6l3nqpf723hf7@3fns3z5cjqk4>
Date: Wed, 5 Mar 2025 10:04:25 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>
Cc: Thomas Gleixner <tglx@...utronix.de>, 
	Claudio Carvalho <cclaudio@...ux.ibm.com>, Peter Huewe <peterhuewe@....de>, x86@...nel.org, 
	Dov Murik <dovmurik@...ux.ibm.com>, linux-coco@...ts.linux.dev, 
	Dionna Glaze <dionnaglaze@...gle.com>, James Bottomley <James.Bottomley@...senpartnership.com>, 
	Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>, Jason Gunthorpe <jgg@...pe.ca>, 
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class_ops

On Tue, Mar 04, 2025 at 10:21:55PM +0200, Jarkko Sakkinen wrote:
>On Tue, Mar 04, 2025 at 06:56:02PM +0200, Jarkko Sakkinen wrote:
>> On Mon, 2025-03-03 at 17:21 +0100, Stefano Garzarella wrote:
>> > On Sat, Mar 01, 2025 at 03:45:10AM +0200, Jarkko Sakkinen wrote:
>> > > On Fri, Feb 28, 2025 at 06:07:17PM +0100, Stefano Garzarella wrote:
>> > > > +	int (*send_recv)(struct tpm_chip *chip, u8 *buf, size_t
>> > > > buf_len,
>> > > > +			 size_t to_send);
>> > >
>> > > Please describe the meaning and purpose of to_send.
>> >
>> > Sure, I'll add in the commit description.
>>
>> It's always a command, right? So better be more concerete than
>> "to_send", e.g. "cmd_len".

Right!

>>
>> I'd do instead:
>>
>> if (!chip->send)
>> 	goto out_recv;
>>
>> And change recv into:
>>
>> int (*recv)(struct tpm_chip *chip, u8 *buf, size_t buf_len,
>> 	    cmd_len);
>
>I think I went here over the top, and *if* we need a new callback
>putting send_recv would be fine. Only thing I'd take from this is to
>rename to_len as cmd_len.

Got it.

>
>However, I don't think there are strong enough reasons to add complexity
>to the callback interface with the basis of this single driver. You
>should deal with this internally inside the driver instead.
>
>So do something along the lines of, e.g.:
>
>1. Create dummy send() copying the command to internal
>   buffer.
>2. Create ->status() returning zero, and set req_complete_mask and
>   req_complete_val to zero.
>3. Performan transaction in recv().
>
>How you split send_recv() between send() and recv() is up to you. This
>was merely showing that we don't need send_recv() desperately.

We did something similar in v1 [1], but instead of your point 2, we just 
set `chip->flags |= TPM_CHIP_FLAG_IRQ;` in the probe() after we 
allocated the chip.

Jason suggested the send_recv() ops [2], which I liked, but if you 
prefer to avoid that, I can restore what we did in v1 and replace the 
TPM_CHIP_FLAG_IRQ hack with your point 2 (or use TPM_CHIP_FLAG_IRQ if 
you think it is fine).

@Jarkko, @Jason, I don't have a strong preference about it, so your 
choice :-)

Thanks,
Stefano

[1] https://lore.kernel.org/linux-integrity/20241210143423.101774-2-sgarzare@redhat.com/
[2] https://lore.kernel.org/linux-integrity/CAGxU2F51EoqDqi6By6eBa7qT+VT006DJ9+V-PANQ6GQrwVWt_Q@mail.gmail.com/