[Xen-changelog] [xen master] docs/vtpm: explain dom0 physical TPM access caveats

[patchbot@xxxxxxx]

commit 2fb930dd374669a7618cd79998975201fc31c745
Author:     Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
AuthorDate: Wed Mar 12 10:37:40 2014 -0400
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Fri Mar 14 11:00:20 2014 +0000

    docs/vtpm: explain dom0 physical TPM access caveats
    
    Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 docs/misc/vtpm.txt |   22 ++++++++++++++++++----
 1 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/docs/misc/vtpm.txt b/docs/misc/vtpm.txt
index df1dfae..d20b424 100644
--- a/docs/misc/vtpm.txt
+++ b/docs/misc/vtpm.txt
@@ -120,10 +120,24 @@ the stubdom tree.
 Compiling the LINUX dom0 kernel:
 --------------------------------
 
-The Linux dom0 kernel should not try accessing the TPM while the vTPM
-Manager domain is accessing it; the simplest way to accomplish this is
-to ensure the kernel is compiled without a driver for the TPM, or avoid
-loading the driver by blacklisting the module.
+Because the TPM manager uses direct access to the physical TPM, it may 
interfere
+with access to the TPM by dom0.  The simplest solution for this is to prevent
+dom0 from accessing the physical TPM by compiling the kernel without a driver 
or
+blacklisting the module.  If dom0 needs a TPM but does not need to use it 
during
+the boot process (i.e. it is not using IMA), a virtual TPM can be attached to
+dom0 after the system is booted.
+
+Because the TPM manager does not yet accept requests for deep quotes, if a 
quote
+or other request needs to be fulfilled by the physical TPM, dom0 will need to
+access the physical TPM.  In order to prevent interference, the TPM Manager and
+dom0 should use different values for the TPM's locality; since Linux always 
uses
+locality 0, using locality 2 for the TPM Manager is recommended.  If both Linux
+and the TPM Manager attempt to access the TPM at the same time, the TPM device
+will return a busy status; some applications will consider this a fatal error
+instead of retrying the command at a later time.  If a vTPM gets an error when
+loading its key, it will currently generate a fresh vTPM image (with a new EK,
+SRK, and blank NVRAM).
+
 
 Compiling the LINUX domU kernel:
 --------------------------------
--
generated by git-patchbot for /home/xen/git/xen.git#master

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