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From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: linux-integrity@vger.kernel.org, Mimi Zohar <zohar@linux.ibm.com>,
	Jerry Snitselaar <jsnitsel@redhat.com>,
	Sumit Garg <sumit.garg@linaro.org>,
	Stefan Berger <stefanb@linux.vnet.ibm.com>,
	Peter Huewe <peterhuewe@gmx.de>, Jason Gunthorpe <jgg@ziepe.ca>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/2] tpm: Detach page allocation from tpm_buf
Date: Fri, 4 Oct 2019 22:01:04 +0300	[thread overview]
Message-ID: <20191004190104.GK6945@linux.intel.com> (raw)
In-Reply-To: <1570207062.3563.17.camel@HansenPartnership.com>

On Fri, Oct 04, 2019 at 09:37:42AM -0700, James Bottomley wrote:
> On Thu, 2019-10-03 at 21:51 +0300, Jarkko Sakkinen wrote:
> > As has been seen recently, binding the buffer allocation and tpm_buf
> > together is sometimes far from optimal.
> 
> Can you elaborate on this a bit more?  I must have missed the
> discussion.
> 
> >  The buffer might come from the caller namely when tpm_send() is used
> > by another subsystem. In addition we can stability in call sites w/o
> > rollback (e.g. power events)>
> > 
> > Take allocation out of the tpm_buf framework and make it purely a
> > wrapper for the data buffer.
> 
> What you're doing here is taking a single object with a single lifetime
> and creating two separate objects with separate lifetimes and a
> dependency.  The problem with doing that is that it always creates
> subtle and hard to debug corner cases where the dependency gets
> violated, so it's usually better to simplify the object lifetimes by
> reducing the dependencies and combining as many dependent objects as
> possible into a single object with one lifetime.  Bucking this trend
> for a good reason is OK, but I think a better reason than "is sometimes
> far from optimal" is needed.

Right, I see your point. We can just say instead in a comment that
tpm_buf_init() is optional if you need to allocate the buffer and
do not provide your own.

Thanks for the remark. I have to agree with this.

/Jarkko

      parent reply	other threads:[~2019-10-04 19:01 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 18:51 [PATCH v3 0/2] tpm: Detach page allocation from tpm_buf Jarkko Sakkinen
2019-10-03 18:51 ` [PATCH v3 1/2] tpm: Use GFP_KERNEL for allocating struct tpm_buf Jarkko Sakkinen
2019-10-04  0:25   ` James Bottomley
2019-10-06 10:03     ` Jarkko Sakkinen
2019-10-07 19:12       ` James Bottomley
2019-10-07 23:43         ` Jerry Snitselaar
2019-10-08 22:52         ` Jarkko Sakkinen
2019-10-09 21:36         ` Jarkko Sakkinen
2019-10-11 16:03           ` James Bottomley
2019-10-03 18:51 ` [PATCH v3 2/2] tpm: Detach page allocation from tpm_buf Jarkko Sakkinen
2019-10-04 16:37   ` James Bottomley
2019-10-04 17:37     ` Mimi Zohar
2019-10-04 17:41       ` James Bottomley
2019-10-04 18:24         ` Jerry Snitselaar
2019-10-06 23:32           ` Jarkko Sakkinen
2019-10-04 19:01     ` Jarkko Sakkinen [this message]

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