Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: i0GOb7Bk8vNt0ltnzeAq8kW2igZ5pdSLzHeWVGhJ72n5xOH5rt7q/avs3/Xh1n9VPadq6wYz0n
 fF4LwP6WnYoA==
IronPort-SDR: xBXPaVJZ/1VjL78CnhmPGTxk4I1uFJ9lQe+ZjEYTD1W5JKBaxO6P/o41jt7j+5z1oOICEkocd9
 cCgAtnDJJ0kg==
Date:   Thu, 2 Jul 2020 22:54:26 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Stefan Berger <stefanb@linux.ibm.com>
Cc:     linux-integrity@vger.kernel.org,
        James Bottomley <James.Bottomley@HansenPartnership.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jerry Snitselaar <jsnitsel@redhat.com>,
        Sumit Garg <sumit.garg@linaro.org>,
        Alexey Klimov <aklimov@redhat.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] tpm: tpm2-space: Resize session and context buffers
 dynamically
Message-ID: <20200702195426.GA31291@linux.intel.com>
References: <20200625043819.376693-1-jarkko.sakkinen@linux.intel.com>
 <8d19d5e2-91bc-09ad-6b94-d51a7aad6376@linux.ibm.com>
 <20200625212556.GC20341@linux.intel.com>
 <031020b9-dc0a-3c2f-32e4-4bb2db4b5a2b@linux.ibm.com>
 <20200626114815.GA5847@linux.intel.com>
 <5d786bca-6a0f-0c7f-e856-04dac2f280f6@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5d786bca-6a0f-0c7f-e856-04dac2f280f6@linux.ibm.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jun 26, 2020 at 08:16:45AM -0400, Stefan Berger wrote:
> On 6/26/20 7:48 AM, Jarkko Sakkinen wrote:
> > 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@HansenPartnership.com>
> > > > > > Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
> > > > > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.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.
> 
> 16kb is plenty of space for years to come. Maybe just enlarge the buffer for
> the regression and then do dynamic allocation as the final solution for the
> tip. I can try to test compile it on one or two long term stable kernels.
> Hopefully it applies cleanly. Simple test just in case you had a setup with
> a VM and libtpms master:

3*4096 bytes is based on absolutely nothing.

The chosen page size is based on the PPC64 default page size.

/Jarkko