On Mon, Dec 07, 2020 at 12:01:09PM +0000, Robin Murphy wrote: > On 2020-12-05 08:29, Keqian Zhu wrote: > > ... then we have more chance to detect wrong code logic. > > I don't follow that justification - it's still the same check with the same > outcome, so how does moving it have any effect on the chance to detect > errors? > > AFAICS the only difference it would make is to make some errors *less* > obvious - if a sufficiently broken caller passes an empty prot value > alongside an invalid size or already-mapped address, this will now quietly > hide the warnings from the more serious condition(s). > > Yes, it will bail out a bit faster in the specific case where the prot value > is the only thing wrong, but since when do we optimise for fundamentally > incorrect API usage?
I thought it was the other way round -- doesn't this patch move the "empty prot" check later, so we have a chance to check the size and addresses first? Will > > Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com> > > --- > > drivers/iommu/io-pgtable-arm.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c > > index a7a9bc08dcd1..8ade72adab31 100644 > > --- a/drivers/iommu/io-pgtable-arm.c > > +++ b/drivers/iommu/io-pgtable-arm.c > > @@ -444,10 +444,6 @@ static int arm_lpae_map(struct io_pgtable_ops *ops, > > unsigned long iova, > > arm_lpae_iopte prot; > > long iaext = (s64)iova >> cfg->ias; > > - /* If no access, then nothing to do */ > > - if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE))) > > - return 0; > > - > > if (WARN_ON(!size || (size & cfg->pgsize_bitmap) != size)) > > return -EINVAL; > > @@ -456,6 +452,10 @@ static int arm_lpae_map(struct io_pgtable_ops *ops, > > unsigned long iova, > > if (WARN_ON(iaext || paddr >> cfg->oas)) > > return -ERANGE; > > + /* If no access, then nothing to do */ > > + if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE))) > > + return 0; > > + > > prot = arm_lpae_prot_to_pte(data, iommu_prot); > > ret = __arm_lpae_map(data, iova, paddr, size, prot, lvl, ptep, gfp); > > /* > >
