3 files changed, 129 insertions, 0 deletions

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index e5d0c28372ea..75e5c40f80a5 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -161,6 +161,20 @@ config XEN_GRANT_DEV_ALLOC
           to other domains. This can be used to implement frontend drivers
           or as part of an inter-domain shared memory channel.
 
+config XEN_GRANT_DMA_ALLOC
+        bool "Allow allocating DMA capable buffers with grant reference module"
+        depends on XEN && HAS_DMA
+        help
+          Extends grant table module API to allow allocating DMA capable
+          buffers and mapping foreign grant references on top of it.
+          The resulting buffer is similar to one allocated by the balloon
+          driver in that proper memory reservation is made by
+          ({increase|decrease}_reservation and VA mappings are updated if
+          needed).
+          This is useful for sharing foreign buffers with HW drivers which
+          cannot work with scattered buffers provided by the balloon driver,
+          but require DMAable memory instead.
+
 config SWIOTLB_XEN
         def_bool y
         select SWIOTLB
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index bb4840653bf2..7bafa703a992 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -45,6 +45,9 @@
 #include <linux/workqueue.h>
 #include <linux/ratelimit.h>
 #include <linux/moduleparam.h>
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+#include <linux/dma-mapping.h>
+#endif
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
@@ -57,6 +60,7 @@
 #ifdef CONFIG_X86
 #include <asm/xen/cpuid.h>
 #endif
+#include <xen/mem-reservation.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/interface.h>
 
@@ -838,6 +842,99 @@ void gnttab_free_pages(int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL_GPL(gnttab_free_pages);
 
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+/**
+ * gnttab_dma_alloc_pages - alloc DMAable pages suitable for grant mapping into
+ * @args: arguments to the function
+ */
+int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
+{
+        unsigned long pfn, start_pfn;
+        size_t size;
+        int i, ret;
+
+        size = args->nr_pages << PAGE_SHIFT;
+        if (args->coherent)
+                args->vaddr = dma_alloc_coherent(args->dev, size,
+                                                 &args->dev_bus_addr,
+                                                 GFP_KERNEL | __GFP_NOWARN);
+        else
+                args->vaddr = dma_alloc_wc(args->dev, size,
+                                           &args->dev_bus_addr,
+                                           GFP_KERNEL | __GFP_NOWARN);
+        if (!args->vaddr) {
+                pr_debug("Failed to allocate DMA buffer of size %zu\n", size);
+                return -ENOMEM;
+        }
+
+        start_pfn = __phys_to_pfn(args->dev_bus_addr);
+        for (pfn = start_pfn, i = 0; pfn < start_pfn + args->nr_pages;
+                        pfn++, i++) {
+                struct page *page = pfn_to_page(pfn);
+
+                args->pages[i] = page;
+                args->frames[i] = xen_page_to_gfn(page);
+                xenmem_reservation_scrub_page(page);
+        }
+
+        xenmem_reservation_va_mapping_reset(args->nr_pages, args->pages);
+
+        ret = xenmem_reservation_decrease(args->nr_pages, args->frames);
+        if (ret != args->nr_pages) {
+                pr_debug("Failed to decrease reservation for DMA buffer\n");
+                ret = -EFAULT;
+                goto fail;
+        }
+
+        ret = gnttab_pages_set_private(args->nr_pages, args->pages);
+        if (ret < 0)
+                goto fail;
+
+        return 0;
+
+fail:
+        gnttab_dma_free_pages(args);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(gnttab_dma_alloc_pages);
+
+/**
+ * gnttab_dma_free_pages - free DMAable pages
+ * @args: arguments to the function
+ */
+int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args)
+{
+        size_t size;
+        int i, ret;
+
+        gnttab_pages_clear_private(args->nr_pages, args->pages);
+
+        for (i = 0; i < args->nr_pages; i++)
+                args->frames[i] = page_to_xen_pfn(args->pages[i]);
+
+        ret = xenmem_reservation_increase(args->nr_pages, args->frames);
+        if (ret != args->nr_pages) {
+                pr_debug("Failed to decrease reservation for DMA buffer\n");
+                ret = -EFAULT;
+        } else {
+                ret = 0;
+        }
+
+        xenmem_reservation_va_mapping_update(args->nr_pages, args->pages,
+                                             args->frames);
+
+        size = args->nr_pages << PAGE_SHIFT;
+        if (args->coherent)
+                dma_free_coherent(args->dev, size,
+                                  args->vaddr, args->dev_bus_addr);
+        else
+                dma_free_wc(args->dev, size,
+                            args->vaddr, args->dev_bus_addr);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(gnttab_dma_free_pages);
+#endif
+
 /* Handling of paged out grant targets (GNTST_eagain) */
 #define MAX_DELAY 256
 static inline void
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index de03f2542bb7..9bc5bc07d4d3 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -198,6 +198,24 @@ void gnttab_free_auto_xlat_frames(void);
 int gnttab_alloc_pages(int nr_pages, struct page **pages);
 void gnttab_free_pages(int nr_pages, struct page **pages);
 
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+struct gnttab_dma_alloc_args {
+        /* Device for which DMA memory will be/was allocated. */
+        struct device *dev;
+        /* If set then DMA buffer is coherent and write-combine otherwise. */
+        bool coherent;
+
+        int nr_pages;
+        struct page **pages;
+        xen_pfn_t *frames;
+        void *vaddr;
+        dma_addr_t dev_bus_addr;
+};
+
+int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args);
+int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args);
+#endif
+
 int gnttab_pages_set_private(int nr_pages, struct page **pages);
 void gnttab_pages_clear_private(int nr_pages, struct page **pages);