On Fri, Sep 13, 2019 at 03:44:12PM -0700, Doug Anderson wrote: > On Fri, Sep 13, 2019 at 4:48 AM Robin Murphy <[email protected]> wrote: > > > > Although CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT is a welcome tool > > for smoking out inadequate firmware, the failure mode is non-obvious > > and can be confusing for end users. Add some special-case reporting of > > Unidentified Stream Faults to help clarify this particular symptom. > > > > CC: Douglas Anderson <[email protected]> > > nit that I believe that "Cc" (lowercase 2nd c) is correct. > > > Signed-off-by: Robin Murphy <[email protected]> > > --- > > drivers/iommu/arm-smmu.c | 5 +++++ > > drivers/iommu/arm-smmu.h | 2 ++ > > 2 files changed, 7 insertions(+) > > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > > index b7cf24402a94..76ac8c180695 100644 > > --- a/drivers/iommu/arm-smmu.c > > +++ b/drivers/iommu/arm-smmu.c > > @@ -499,6 +499,11 @@ static irqreturn_t arm_smmu_global_fault(int irq, void > > *dev) > > dev_err_ratelimited(smmu->dev, > > "\tGFSR 0x%08x, GFSYNR0 0x%08x, GFSYNR1 0x%08x, GFSYNR2 > > 0x%08x\n", > > gfsr, gfsynr0, gfsynr1, gfsynr2); > > + if (IS_ENABLED(CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT) && > > + (gfsr & sGFSR_USF)) > > + dev_err_ratelimited(smmu->dev, > > + "Stream ID %hu may not be described by firmware, > > try booting with \"arm-smmu.disable_bypass=0\"\n", > > + (u16)gfsynr1); > > In general it seems like a sane idea to surface an error like this. I > guess a few nits: > > 1. "By firmware" might be a bit misleading. In most cases I'm aware > of the problem is in the device tree that was bundled together with > the kernel. If there are actually cases where firmware has baked in a > device tree and it got this wrong then we might want to spend time > figuring out what to do about it.
I thought that was usually the way UEFI systems worked, where the kernel is updated independently of the device-tree? Either way, that should be what we're aiming for, even if many platforms require the two to be tied together. > 2. Presumably booting with "arm-smmu.disable_bypass=0" is in most > cases the least desirable option available. I always consider kernel > command line parameters as something of a last resort for > configuration and would only be something that and end user might do > if they were given a kernel compiled by someone else (like if someone > where taking a prebuilt Linux distro and trying to install it onto a > generic PC). Are you seeing cases where this is happening? If people > are compiling their own kernel I'd argue that telling them to set > "CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT" to "no" is much better > than trying to jam a command line option on. Command line options > don't scale well. Hmm. Recompiling seems like even more of a last resort to me! > 3. Any chance you could make it more obvious that this change is > undesirable and a last resort? AKA: > > "Stream ID x blocked for security reasons; allow anyway by booting > with arm-smmu.disable_bypass=0" How about: "Blocked transaction from unknown Stream ID x; boot with \"arm-smmu.disable_bypass=0\" to allow these transactions, although this may have security implications." Will _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
