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Subject[RFC PATCH 2/2] xen/grant-table: Use unpopulated DMAable pages instead of real RAM ones
Date
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Depends on CONFIG_XEN_UNPOPULATED_ALLOC. If enabled then unpopulated
DMAable (contiguous) pages will be allocated for grant mapping into
instead of ballooning out real RAM pages.

TODO: Fallback to real RAM pages if xen_alloc_unpopulated_dma_pages()
fails.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
drivers/xen/grant-table.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 8ccccac..2bb4392 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -864,6 +864,25 @@ EXPORT_SYMBOL_GPL(gnttab_free_pages);
*/
int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
{
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+ int ret;
+
+ ret = xen_alloc_unpopulated_dma_pages(args->dev, args->nr_pages,
+ args->pages);
+ if (ret < 0)
+ return ret;
+
+ ret = gnttab_pages_set_private(args->nr_pages, args->pages);
+ if (ret < 0) {
+ gnttab_dma_free_pages(args);
+ return ret;
+ }
+
+ args->vaddr = page_to_virt(args->pages[0]);
+ args->dev_bus_addr = page_to_phys(args->pages[0]);
+
+ return ret;
+#else
unsigned long pfn, start_pfn;
size_t size;
int i, ret;
@@ -910,6 +929,7 @@ int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
fail:
gnttab_dma_free_pages(args);
return ret;
+#endif
}
EXPORT_SYMBOL_GPL(gnttab_dma_alloc_pages);

@@ -919,6 +939,12 @@ EXPORT_SYMBOL_GPL(gnttab_dma_alloc_pages);
*/
int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args)
{
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+ gnttab_pages_clear_private(args->nr_pages, args->pages);
+ xen_free_unpopulated_dma_pages(args->dev, args->nr_pages, args->pages);
+
+ return 0;
+#else
size_t size;
int i, ret;

@@ -946,6 +972,7 @@ int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args)
dma_free_wc(args->dev, size,
args->vaddr, args->dev_bus_addr);
return ret;
+#endif
}
EXPORT_SYMBOL_GPL(gnttab_dma_free_pages);
#endif
--
2.7.4
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