linux-kernel - Re: [RFC PATCH 6/6] iommu/arm-smmu-v3: Avoid ILLEGAL setting of STE.S1STALLD and CD.S

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Message-ID: <20170913030643.GD12411@arm.com>
Date:   Wed, 13 Sep 2017 04:06:44 +0100
From:   Will Deacon <will.deacon@....com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     Yisheng Xie <xieyisheng1@...wei.com>, joro@...tes.org,
        robh+dt@...nel.org, mark.rutland@....com,
        lorenzo.pieralisi@....com, hanjun.guo@...aro.org,
        sudeep.holla@....com, rjw@...ysocki.net, lenb@...nel.org,
        robin.murphy@....com, robert.moore@...el.com, lv.zheng@...el.com,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devel@...ica.org,
        liubo95@...wei.com, chenjiankang1@...wei.com, xieyisheng@...wei.com
Subject: Re: [RFC PATCH 6/6] iommu/arm-smmu-v3: Avoid ILLEGAL setting of
 STE.S1STALLD and CD.S

On Tue, Sep 05, 2017 at 01:54:19PM +0100, Jean-Philippe Brucker wrote:
> On 31/08/17 09:20, Yisheng Xie wrote:
> > It is ILLEGAL to set STE.S1STALLD if STALL_MODEL is not 0b00, which
> > means we should not disable stall mode if stall/terminate mode is not
> > configuable.
> > 
> > Meanwhile, it is also ILLEGAL when STALL_MODEL==0b10 && CD.S==0 which
> > means if stall mode is force we should always set CD.S.
> > 
> > This patch add ARM_SMMU_FEAT_TERMINATE feature bit for smmu, and use
> > TERMINATE feature checking to ensue above ILLEGAL cases from happening.
> > 
> > Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
> > ---
> >  drivers/iommu/arm-smmu-v3.c | 22 ++++++++++++++++------
> >  1 file changed, 16 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> > index dbda2eb..0745522 100644
> > --- a/drivers/iommu/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm-smmu-v3.c
> > @@ -55,6 +55,7 @@
> >  #define IDR0_STALL_MODEL_SHIFT		24
> >  #define IDR0_STALL_MODEL_MASK		0x3
> >  #define IDR0_STALL_MODEL_STALL		(0 << IDR0_STALL_MODEL_SHIFT)
> > +#define IDR0_STALL_MODEL_NS		(1 << IDR0_STALL_MODEL_SHIFT)
> >  #define IDR0_STALL_MODEL_FORCE		(2 << IDR0_STALL_MODEL_SHIFT)
> >  #define IDR0_TTENDIAN_SHIFT		21
> >  #define IDR0_TTENDIAN_MASK		0x3
> > @@ -766,6 +767,7 @@ struct arm_smmu_device {
> >  #define ARM_SMMU_FEAT_SVM		(1 << 15)
> >  #define ARM_SMMU_FEAT_HA		(1 << 16)
> >  #define ARM_SMMU_FEAT_HD		(1 << 17)
> > +#define ARM_SMMU_FEAT_TERMINATE		(1 << 18)
> 
> I'd rather introduce something like "ARM_SMMU_FEAT_STALL_FORCE" instead.
> Terminate model has another meaning, and is defined by a different bit in
> IDR0.

Yes. What we need to do is:

- If STALL_MODEL is 0b00, then set S1STALLD
- If STALL_MODEL is 0b01, then we're ok (in future, avoiding trying to use
  stalls, even for masters that claim to support it)
- If STALL_MODEL is 0b10, then force all PCI devices and any platform
  devices that don't claim to support stalls into bypass (depending on
  disable_bypass).

Reasonable? We could actually knock up a fix for mainline to do most of
this already.

Will