linux-kernel - Re: [PATCH 1/2] iommu/io-pgtable-arm: Implement .iotlb_sync

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Message-ID: <aNsHCKdfzQNh9GFj@google.com>
Date: Mon, 29 Sep 2025 22:24:08 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Daniel Mentz <danielmentz@...gle.com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Will Deacon <will@...nel.org>, Mostafa Saleh <smostafa@...gle.com>,
	Liviu Dudau <liviu.dudau@....com>, Jason Gunthorpe <jgg@...dia.com>,
	Rob Clark <robin.clark@....qualcomm.com>
Subject: Re: [PATCH 1/2] iommu/io-pgtable-arm: Implement .iotlb_sync_map
 callback

On Mon, Sep 29, 2025 at 01:42:29PM -0700, Daniel Mentz wrote:
> On Mon, Sep 29, 2025 at 12:57 PM Pranjal Shrivastava <praan@...gle.com> wrote:
> >
> > On Sat, Sep 27, 2025 at 10:39:52PM +0000, Daniel Mentz wrote:
> > > +static int __arm_lpae_iotlb_sync_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
> > > +                           size_t size, int lvl, arm_lpae_iopte *ptep)
> > > +{
> > > +     struct io_pgtable *iop = &data->iop;
> > > +     size_t block_size = ARM_LPAE_BLOCK_SIZE(lvl, data);
> > > +     int ret = 0, num_entries, max_entries;
> > > +     unsigned long iova_offset, sync_idx_start, sync_idx_end;
> > > +     int i, shift, synced_entries = 0;
> > > +
> > > +     shift = (ARM_LPAE_LVL_SHIFT(lvl - 1, data) + ARM_LPAE_PGD_IDX(lvl - 1, data));
> > > +     iova_offset = iova & ((1ULL << shift) - 1);
> > > +     sync_idx_start = ARM_LPAE_LVL_IDX(iova, lvl, data);
> > > +     sync_idx_end = (iova_offset + size + block_size - ARM_LPAE_GRANULE(data)) >>
> > > +             ARM_LPAE_LVL_SHIFT(lvl, data);
> > > +     max_entries = arm_lpae_max_entries(sync_idx_start, data);
> > > +     num_entries = min_t(unsigned long, sync_idx_end - sync_idx_start, max_entries);
> > > +     ptep += sync_idx_start;
> > > +
> > > +     if (lvl < (ARM_LPAE_MAX_LEVELS - 1)) {
> > > +             for (i = 0; i < num_entries; i++) {
> > > +                     arm_lpae_iopte pte = READ_ONCE(ptep[i]);
> > > +                     unsigned long synced;
> > > +
> > > +                     WARN_ON(!pte);
> > > +
> > > +                     if (iopte_type(pte) == ARM_LPAE_PTE_TYPE_TABLE) {
> > > +                             int n = i - synced_entries;
> > > +
> > > +                             if (n) {
> > > +                                     __arm_lpae_sync_pte(&ptep[synced_entries], n, &iop->cfg);
> > > +                                     synced_entries += n;
> > > +                             }
> > > +                             ret = __arm_lpae_iotlb_sync_map(data, iova, size, lvl + 1,
> > > +                                                             iopte_deref(pte, data));
> >
> > I think we must check the returned value here and break the loop on
> > error. Otherwise, we might burry a failure by continuing the loop.
> > We should add something like:
> >
> > if (ret)
> >         break;
> >
> 
> Now, I'm realising that __arm_lpae_iotlb_sync_map always returns 0, in
> which case I could change the return type to void. Would that work for
> you?

Ah, yes, I just realized that too. I guess we can simply change the
return type to void.

Thanks,
Praan