Hi, On 2020/12/7 20:05, Will Deacon wrote: > 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? Yes, this is my original idea. For that we treat iommu_prot with no permission as success at early start, defer this early return can expose hidden errors. Thanks, Keqian > > 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); >>> /* >>> > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
