Messages in this thread | | | Date | Sun, 5 Jul 2009 22:26:46 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC v6][PATCH 4/4] intel_txt: force IOMMU on for Intel(R) TXT launch |
| |
* Pavel Machek <pavel@ucw.cz> wrote:
> On Fri 2009-07-03 10:21:11, Ingo Molnar wrote: > > > > * Pavel Machek <pavel@ucw.cz> wrote: > > > > > > > > On Tue 2009-06-30 19:31:10, Joseph Cihula wrote: > > > > The tboot module will DMA protect all of memory in order to ensure the that > > > > kernel will be able to initialize without compromise (from DMA). Consequently, > > > > the kernel must enable Intel(R) Virtualization Technology for Directed I/O > > > > (VT-d or Intel IOMMU) in order to replace this broad protection with the > > > > appropriate page-granular protection. Otherwise DMA devices will be unable > > > > to read or write from memory and the kernel will eventually panic. > > > > > > > > Because runtime IOMMU support is configurable by command line options, this > > > > patch will force it to be enabled regardless of the options specified, and will > > > > log a message if it was required to force it on. > > > > > > > > > > > > dmar.c | 7 +++++++ > > > > intel-iommu.c | 17 +++++++++++++++-- > > > > 2 files changed, 22 insertions(+), 2 deletions(-) > > > > > > > > Signed-off-by: Joseph Cihula <joseph.cihula@intel.com> > > > > Signed-off-by: Shane Wang <shane.wang@intel.com> > > > > > > NAK. Breaks user expectations, misses docs updates. > > > > What's your proposed solution? If an incompatible IOMMU option > > is specified should the kernel to disable TXT and panic? > > Yes. > > ...and whether we decide one way or another, it needs to be > documented.a
But the user already specified another thing as well: that we should boot with TXT.
So we have conflicting user options. Wouldnt it be the proper engineering solution to print a warning about the incompatible IOMMU option and disable it, but not crash the bootup? We generally prefer to boot up.
Anyway, this is a small detail clearly.
Ingo
| |