Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command

[Will Deacon]

Hi Robin,

On Mon, Aug 07, 2023 at 08:20:45PM +0100, Robin Murphy wrote:
> On 2023-08-06 06:28, zhurui wrote:
> > On 2023/8/5 2:30, Nicolin Chen wrote:
> > > On Fri, Aug 04, 2023 at 05:52:25PM +0100, Will Deacon wrote:
> > > > On Fri, Aug 04, 2023 at 05:31:20PM +0800, zhurui wrote:
> > > > > When tg != 0 but ttl, scale, num all 0 in a range tlbi command, it
> > > > > is reserved and will cause the CERROR_ILL error. This case means
> > > > > that the size to be invalidated is only one page size, and the
> > > > > range invalidation is meaningless here. So we set tg to 0 in this
> > > > > case to do an non-range invalidation instead.
> > > 
> > > > > @@ -1930,6 +1927,12 @@ static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd,
> > > > >                          num = (num_pages >> scale) & CMDQ_TLBI_RANGE_NUM_MAX;
> > > > >                          cmd->tlbi.num = num - 1;
> > > > > 
> > > > > +                       /* Prevent error caused by one page tlbi with leaf 0 */
> > > > > +                       if (scale == 0 && num == 1 && cmd->tlbi.leaf == 0)
> > > > > +                               cmd->tlbi.tg = 0;
> > > > 
> > > > This should only be true for the last iteration, right (i.e. when num_pages
> > > > == 1)? In which case, I'd prefer to leave the old code as-is and just add:
> > > > 
> > > >          /* Single-page leaf invalidation requires a TG field of 0 */
> > > >          if (num_pages == 1 && !cmd->tlbi.leaf)
> > > >                  cmd->tlbi.tg = 0;To Will and Nicolin,
> > 
> > Not only the last iteration, it's the result of __ffs function. For example, if
> > numpages is 33, then the value of __ffs(num_pages) is 0, so the value of scale
> > is also 0. The value of num depends on CMDQ_TLBI_RANGE_NUM_MAX. That is, the
> > maximum value of num is 31. Therefore, the final value of num is 1.
> > So, if consider CMDQ_TLBI_RANGE_NUM_MAX, there will be some case not the last
> > one page but the beginning pages. That's why I use scale and num as conditions,
> > not num_pages. Then I should reassign tg based on the result.
> 
> Yeah, I'd rather not downgrade to a non-range invalidate since that
> complicates the reasoning for the errata affecting those. If the size of the
> invalidation is equal to TG then it can only represent a single last-level
> page, i.e. TTL=3, thus if it does warrant handling here then indeed
> rearranging to base the condition on num_pages as well ought to suffice.
> However, this is all still begging the question of where and why we're doing
> a *non-leaf* invalidation that isn't aligned to the size of a table, because
> that in itself doesn't make a whole heap of sense - my hunch is that that
> wants figuring out and could probably be fixed at the source.

Isn't that described above because we're using CMDQ_TLBI_RANGE_NUM_MAX
to break up the range into separate commands?

Do you mind if I queue the patch as-is for now? I don't think the driver
should be emitting illegal commands, and v2 of the patch does seem like
the obvious thing to do.

Will