Subject: Re: [PATCH kernel v10 11/34] vfio: powerpc/spapr: Moving pinning/unpinning to helpers

From: Gavin Shan <[email-masked]>
Date: Wed, 13 May 2015 16:32:42 +1000

On Tue, May 12, 2015 at 01:39:00AM +1000, Alexey Kardashevskiy wrote:
>This is a pretty mechanical patch to make next patches simpler.
>
>New tce_iommu_unuse_page() helper does put_page() now but it might skip
>that after the memory registering patch applied.
>
>As we are here, this removes unnecessary checks for a value returned
>by pfn_to_page() as it cannot possibly return NULL.
>
>This moves tce_iommu_disable() later to let tce_iommu_clear() know if
>the container has been enabled because if it has not been, then
>put_page() must not be called on TCEs from the TCE table. This situation
>is not yet possible but it will after KVM acceleration patchset is
>applied.
>
>This changes code to work with physical addresses rather than linear
>mapping addresses for better code readability. Following patches will
>add an xchg() callback for an IOMMU table which will accept/return
>physical addresses (unlike current tce_build()) which will eliminate
>redundant conversions.
>
>Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>[aw: for the vfio related changes]
>Acked-by: Alex Williamson <[email-masked]>
>Reviewed-by: David Gibson <[email-masked]>

Reviewed-by: Gavin Shan <[email-masked]>

>---
>Changes:
>v9:
>* changed helpers to work with physical addresses rather than linear
>(for simplicity - later ::xchg() will receive physical and avoid
>additional convertions)
>
>v6:
>* tce_get_hva() returns hva via a pointer
>---
> drivers/vfio/vfio_iommu_spapr_tce.c | 61 +++++++++++++++++++++++++------------
> 1 file changed, 41 insertions(+), 20 deletions(-)
>
>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>index e21479c..115d5e6 100644
>--- a/drivers/vfio/vfio_iommu_spapr_tce.c
>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>@@ -191,69 +191,90 @@ static void tce_iommu_release(void *iommu_data)
> 	struct tce_container *container = iommu_data;
>
> 	WARN_ON(container->tbl && !container->tbl->it_group);
>-	tce_iommu_disable(container);
>
> 	if (container->tbl && container->tbl->it_group)
> 		tce_iommu_detach_group(iommu_data, container->tbl->it_group);
>
>+	tce_iommu_disable(container);
> 	mutex_destroy(&container->lock);
>
> 	kfree(container);
> }
>
>+static void tce_iommu_unuse_page(struct tce_container *container,
>+		unsigned long oldtce)
>+{
>+	struct page *page;
>+
>+	if (!(oldtce & (TCE_PCI_READ | TCE_PCI_WRITE)))
>+		return;
>+

It might be worthy to have a global helper function in iommu.h to check
if the given TCE entry is empty or not, for better readability. I would
think the helper function is used here and there :-)

Thanks,
Gavin

>+	page = pfn_to_page(oldtce >> PAGE_SHIFT);
>+
>+	if (oldtce & TCE_PCI_WRITE)
>+		SetPageDirty(page);
>+
>+	put_page(page);
>+}
>+
> static int tce_iommu_clear(struct tce_container *container,
> 		struct iommu_table *tbl,
> 		unsigned long entry, unsigned long pages)
> {
> 	unsigned long oldtce;
>-	struct page *page;
>
> 	for ( ; pages; --pages, ++entry) {
> 		oldtce = iommu_clear_tce(tbl, entry);
> 		if (!oldtce)
> 			continue;
>
>-		page = pfn_to_page(oldtce >> PAGE_SHIFT);
>-		WARN_ON(!page);
>-		if (page) {
>-			if (oldtce & TCE_PCI_WRITE)
>-				SetPageDirty(page);
>-			put_page(page);
>-		}
>+		tce_iommu_unuse_page(container, oldtce);
> 	}
>
> 	return 0;
> }
>
>+static int tce_iommu_use_page(unsigned long tce, unsigned long *hpa)
>+{
>+	struct page *page = NULL;
>+	enum dma_data_direction direction = iommu_tce_direction(tce);
>+
>+	if (get_user_pages_fast(tce & PAGE_MASK, 1,
>+			direction != DMA_TO_DEVICE, &page) != 1)
>+		return -EFAULT;
>+
>+	*hpa = __pa((unsigned long) page_address(page));
>+
>+	return 0;
>+}
>+
> static long tce_iommu_build(struct tce_container *container,
> 		struct iommu_table *tbl,
> 		unsigned long entry, unsigned long tce, unsigned long pages)
> {
> 	long i, ret = 0;
>-	struct page *page = NULL;
>-	unsigned long hva;
>+	struct page *page;
>+	unsigned long hpa;
> 	enum dma_data_direction direction = iommu_tce_direction(tce);
>
> 	for (i = 0; i < pages; ++i) {
> 		unsigned long offset = tce & IOMMU_PAGE_MASK(tbl) & ~PAGE_MASK;
>
>-		ret = get_user_pages_fast(tce & PAGE_MASK, 1,
>-				direction != DMA_TO_DEVICE, &page);
>-		if (unlikely(ret != 1)) {
>-			ret = -EFAULT;
>+		ret = tce_iommu_use_page(tce, &hpa);
>+		if (ret)
> 			break;
>-		}
>
>+		page = pfn_to_page(hpa >> PAGE_SHIFT);
> 		if (!tce_page_is_contained(page, tbl->it_page_shift)) {
> 			ret = -EPERM;
> 			break;
> 		}
>
>-		hva = (unsigned long) page_address(page) + offset;
>-
>-		ret = iommu_tce_build(tbl, entry + i, hva, direction);
>+		hpa |= offset;
>+		ret = iommu_tce_build(tbl, entry + i, (unsigned long) __va(hpa),
>+				direction);
> 		if (ret) {
>-			put_page(page);
>+			tce_iommu_unuse_page(container, hpa);
> 			pr_err("iommu_tce: %s failed ioba=%lx, tce=%lx, ret=%ld\n",
> 					__func__, entry << tbl->it_page_shift,
> 					tce, ret);
>-- 
>2.4.0.rc3.8.gfb3e7d5
>