linux-kernel - Re: [PATCH v2] tpm: tpm2-space: Resize session and context buffers dynamically

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Message-ID: <20200626114815.GA5847@linux.intel.com>
Date:   Fri, 26 Jun 2020 14:48:15 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Alexey Klimov <aklimov@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tpm: tpm2-space: Resize session and context buffers
 dynamically

On Thu, Jun 25, 2020 at 05:27:50PM -0400, Stefan Berger wrote:
> On 6/25/20 5:25 PM, Jarkko Sakkinen wrote:
> > On Thu, Jun 25, 2020 at 08:41:18AM -0400, Stefan Berger wrote:
> > > On 6/25/20 12:38 AM, Jarkko Sakkinen wrote:
> > > > Re-allocate context and session buffers when needed. Scale them in page
> > > > increments so that the reallocation is only seldomly required, and thus
> > > > causes minimal stress to the system. Add a static maximum limit of four
> > > > pages for buffer sizes.
> > > > 
> > > > Cc: James Bottomley <James.Bottomley@...senPartnership.com>
> > > > Suggested-by: Stefan Berger <stefanb@...ux.ibm.com>
> > > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > > 
> > > You don't want to try a fixes tag? None of the previous versions of this
> > > code will work with newer versions of the TPM 2 then...
> > It's not a regression.
> 
> Ok, so distros will have to backport it.

Now that you mentioned PPC64 in some other email that would make this a
regression since x86 provides less space for keys than PPC64.

I studied PPC64 a bit and it actually allows max 256 kB page size, which
is too much for us, given that there is no accounting implemented for
TPM spaces (so far, should be done eventually).

So to summarize: 0 the idea would decrease the limit on PPC64 and
increase it on ther arch's.  `

Dynamic scaling is over to top for fixing the issue, which means that I
will just define static size of 16 kB for the buffer. We can reconsider
it if we hit the roof again.

/Jarkko