Re: [PATCH v8 5/7] iommu/arm-smmu-v3: Add support for non-strict mode

[Robin Murphy]

On 28/09/18 13:19, Will Deacon wrote:
> On Thu, Sep 20, 2018 at 05:10:25PM +0100, Robin Murphy wrote:
> > From: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> >
> > Now that io-pgtable knows how to dodge strict TLB maintenance, all
> > that's left to do is bridge the gap between the IOMMU core requesting
> > DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE for default domains, and showing the
> > appropriate IO_PGTABLE_QUIRK_NON_STRICT flag to alloc_io_pgtable_ops().
> >
> > Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> > [rm: convert to domain attribute, tweak commit message]
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> > ---
> >
> > v8:
> >   - Use nested switches for attrs
> >   - Document barrier semantics
> >
> >   drivers/iommu/arm-smmu-v3.c | 79 ++++++++++++++++++++++++++-----------
> >   1 file changed, 56 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> > index f10c852479fc..db402e8b068b 100644
> > --- a/drivers/iommu/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm-smmu-v3.c
> > @@ -612,6 +612,7 @@ struct arm_smmu_domain {
> >   	struct mutex			init_mutex; /* Protects smmu pointer */
> >   
> >   	struct io_pgtable_ops		*pgtbl_ops;
> > +	bool				non_strict;
> >   
> >   	enum arm_smmu_domain_stage	stage;
> >   	union {
> > @@ -1407,6 +1408,12 @@ static void arm_smmu_tlb_inv_context(void *cookie)
> >   		cmd.tlbi.vmid	= smmu_domain->s2_cfg.vmid;
> >   	}
> >   
> > +	/*
> > +	 * NOTE: when io-pgtable is in non-strict mode, we may get here with
> > +	 * PTEs previously cleared by unmaps on the current CPU not yet visible
> > +	 * to the SMMU. We are relying on the DSB implicit in queue_inc_prod()
> > +	 * to guarantee those are observed before the TLBI. Do be careful, 007.
> > +	 */
>
> Good, so you can ignore my comment on the previous patch :)

Well, I suppose that comment in io-pgtable *could* have explicitly noted 
that same-CPU order is dealt with elsewhere - feel free to fix it up if 
you think it would be a helpful reminder for the future.

Cheers,
Robin.