| Message ID | 20190710223119.8151-1-robh@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] iommu: io-pgtable: Drop WARN for empty PTEs on unmap | expand |
On Wed, Jul 10, 2019 at 04:31:19PM -0600, Rob Herring wrote: > If a region has been mapped sparsely (such as on page faults), the user > has to keep track of what was mapped or not in order to avoid warnings > when unmapping the entire region. Remove the WARN on empty PTEs to allow > unmapping sparsely mapped regions. > > Cc: Will Deacon <will@kernel.org> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Joerg Roedel <joro@8bytes.org> > Cc: linux-arm-kernel@lists.infradead.org > Cc: iommu@lists.linux-foundation.org > Signed-off-by: Rob Herring <robh@kernel.org> > --- > This is needed for large (up to 1GB AIUI) scratch buffers on panfrost > which are mapped on demand on GPU page faults and can be unmapped on > memory pressure. Alternatively, I'd need to have a bitmap of mapped > pages to track what is mapped or not. Dropping the WARN seems like a > much simpler solution. I suppose an alternative would be to do an iova_to_phys() before you do the unmap(). Would that be acceptable? The WARN_ON() indicates invalid usage by the IOMMU API, so it would be a shame to lose it entirely and I'm hesitant to continue adding quirks at the rate we're currently doing so! Will
On Thu, Jul 11, 2019 at 4:23 AM Will Deacon <will@kernel.org> wrote: > > On Wed, Jul 10, 2019 at 04:31:19PM -0600, Rob Herring wrote: > > If a region has been mapped sparsely (such as on page faults), the user > > has to keep track of what was mapped or not in order to avoid warnings > > when unmapping the entire region. Remove the WARN on empty PTEs to allow > > unmapping sparsely mapped regions. > > > > Cc: Will Deacon <will@kernel.org> > > Cc: Robin Murphy <robin.murphy@arm.com> > > Cc: Joerg Roedel <joro@8bytes.org> > > Cc: linux-arm-kernel@lists.infradead.org > > Cc: iommu@lists.linux-foundation.org > > Signed-off-by: Rob Herring <robh@kernel.org> > > --- > > This is needed for large (up to 1GB AIUI) scratch buffers on panfrost > > which are mapped on demand on GPU page faults and can be unmapped on > > memory pressure. Alternatively, I'd need to have a bitmap of mapped > > pages to track what is mapped or not. Dropping the WARN seems like a > > much simpler solution. > > I suppose an alternative would be to do an iova_to_phys() before you do the > unmap(). Would that be acceptable? Yeah, that should work. Not that efficient, but I don't think releasing the memory is hot path. Thanks, Rob > The WARN_ON() indicates invalid usage by > the IOMMU API, so it would be a shame to lose it entirely and I'm hesitant > to continue adding quirks at the rate we're currently doing so! > > Will
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c index 4e21efbc4459..43971638a5aa 100644 --- a/drivers/iommu/io-pgtable-arm.c +++ b/drivers/iommu/io-pgtable-arm.c @@ -611,7 +611,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, ptep += ARM_LPAE_LVL_IDX(iova, lvl, data); pte = READ_ONCE(*ptep); - if (WARN_ON(!pte)) + if (!pte) return 0; /* If the size matches this level, we're in the right place */
If a region has been mapped sparsely (such as on page faults), the user has to keep track of what was mapped or not in order to avoid warnings when unmapping the entire region. Remove the WARN on empty PTEs to allow unmapping sparsely mapped regions. Cc: Will Deacon <will@kernel.org> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: linux-arm-kernel@lists.infradead.org Cc: iommu@lists.linux-foundation.org Signed-off-by: Rob Herring <robh@kernel.org> --- This is needed for large (up to 1GB AIUI) scratch buffers on panfrost which are mapped on demand on GPU page faults and can be unmapped on memory pressure. Alternatively, I'd need to have a bitmap of mapped pages to track what is mapped or not. Dropping the WARN seems like a much simpler solution. This will need to go thru the DRM tree once I've gotten the panfrost side finished, but wanted some early feedback. Rob drivers/iommu/io-pgtable-arm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)