From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ken Goldman Subject: Re: [tpmdd-devel] [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance. Date: Wed, 13 Sep 2017 14:52:12 -0400 Message-ID: <3c418974-a4c7-518e-b218-f6373c10209e@linux.vnet.ibm.com> References: <20170906125643.5070-1-nayna@linux.vnet.ibm.com> <20170906125643.5070-2-nayna@linux.vnet.ibm.com> <20170906161246.GA9747@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170906161246.GA9747@obsidianresearch.com> Content-Language: en-US Sender: owner-linux-security-module@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, tpmdd-devel@lists.sourceforge.net, linux-ima-devel@lists.sourceforge.net List-Id: tpmdd-devel@lists.sourceforge.net On 9/6/2017 12:12 PM, Jason Gunthorpe wrote: > > The problem with this approach is that the TPM could totally block > the CPU for very long periods of time. > > It seems very risky to enable.. > How would you characterize "very long"? The TPM vendors confirm that they empty the FIFO at internal speeds that are comparable to the bus speed. Thus, any stall will be sub-usec. Is that an issue? In addition, new TPMs have ever larger FIFO's, making stalls less likely going forward.