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

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Message-ID: <CAE2F3rCZhgLOPKMmAqvNaQt3mUdj0kez9_MDxM3nGVOpgr5wuA@mail.gmail.com>
Date: Mon, 29 Sep 2025 13:42:29 -0700
From: Daniel Mentz <danielmentz@...gle.com>
To: Pranjal Shrivastava <praan@...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 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?