On Thu, Sep 5, 2024 at 9:27 AM Robin Murphy <robin.murphy@xxxxxxx> wrote: > > On 05/09/2024 4:53 pm, Will Deacon wrote: > > Hi Rob, > > > > On Thu, Sep 05, 2024 at 05:49:56AM -0700, Rob Clark wrote: > >> From: Rob Clark <robdclark@xxxxxxxxxxxx> > >> > >> This reverts commit 85b715a334583488ad7fbd3001fe6fd617b7d4c0. > >> > >> It was causing gpu smmu faults on x1e80100. > >> > >> I _think_ what is causing this is the change in ordering of > >> __arm_lpae_clear_pte() (dma_sync_single_for_device() on the pgtable > >> memory) and io_pgtable_tlb_flush_walk(). I'm not entirely sure how > >> this patch is supposed to work correctly in the face of other > >> concurrent translations (to buffers unrelated to the one being > >> unmapped(), because after the io_pgtable_tlb_flush_walk() we can have > >> stale data read back into the tlb. > >> > >> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx> > >> --- > >> drivers/iommu/io-pgtable-arm.c | 31 ++++++++++++++----------------- > >> 1 file changed, 14 insertions(+), 17 deletions(-) > > > > Please can you try the diff below, instead? > > Given that the GPU driver's .tlb_add_page is a no-op, I can't see this > making a difference. In fact, given that msm_iommu_pagetable_unmap() > still does a brute-force iommu_flush_iotlb_all() after io-pgtable > returns, and in fact only recently made .tlb_flush_walk start doing > anything either for the sake of the map path, I'm now really wondering > how this patch has had any effect at all... :/ Yeah.. and unfortunately the TBU code only supports two devices so far, so I can't easily repro with TBU enabled atm. Hmm.. __arm_lpae_unmap() is also called in the ->map() path, although not sure how that changes things. BR, -R > > > > Will > > > > --->8 > > > > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c > > index 0e67f1721a3d..0a32e9499e2c 100644 > > --- a/drivers/iommu/io-pgtable-arm.c > > +++ b/drivers/iommu/io-pgtable-arm.c > > @@ -672,7 +672,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, > > /* Clear the remaining entries */ > > __arm_lpae_clear_pte(ptep, &iop->cfg, i); > > > > - if (gather && !iommu_iotlb_gather_queued(gather)) > > + if (!iommu_iotlb_gather_queued(gather)) > > Note that this would reintroduce the latent issue which was present > originally, wherein iommu_iotlb_gather_queued(NULL) is false, but if we > actually allow a NULL gather to be passed to io_pgtable_tlb_add_page() > it may end up being dereferenced (e.g. in arm-smmu-v3). > > Thanks, > Robin. > > > for (int j = 0; j < i; j++) > > io_pgtable_tlb_add_page(iop, gather, iova + j * size, size); > >
