From 36f8abd36febf1c6f67dae26ec7a87be44629138 Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Mon, 11 May 2015 13:44:21 +0100 Subject: [PATCH] xen/biomerge: Don't allow biovec's to be merged when Linux is not using 4KB pages On ARM all dma-capable devices on a same platform may not be protected by an IOMMU. The DMA requests have to use the BFN (i.e MFN on ARM) in order to use correctly the device. While the DOM0 memory is allocated in a 1:1 fashion (PFN == MFN), grant mapping will screw this contiguous mapping. When Linux is using 64KB page granularitary, the page may be split accross multiple non-contiguous MFN (Xen is using 4KB page granularity). Therefore a DMA request will likely fail. Checking that a 64KB page is using contiguous MFN is tedious. For now, always says that biovec are not mergeable. Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini Signed-off-by: David Vrabel --- drivers/xen/biomerge.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c index 8ae2fc90e1ea..4da69dbf7dca 100644 --- a/drivers/xen/biomerge.c +++ b/drivers/xen/biomerge.c @@ -6,10 +6,18 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, const struct bio_vec *vec2) { +#if XEN_PAGE_SIZE == PAGE_SIZE unsigned long bfn1 = pfn_to_bfn(page_to_pfn(vec1->bv_page)); unsigned long bfn2 = pfn_to_bfn(page_to_pfn(vec2->bv_page)); return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && ((bfn1 == bfn2) || ((bfn1+1) == bfn2)); +#else + /* + * XXX: Add support for merging bio_vec when using different page + * size in Xen and Linux. + */ + return 0; +#endif } EXPORT_SYMBOL(xen_biovec_phys_mergeable);