[PATCH v2 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page
From: Konrad Rzeszutek Wilk <hidden>
Date: 2015-07-10 19:13:18
Also in:
lkml
On Thu, Jul 09, 2015 at 09:42:21PM +0100, Julien Grall wrote:
When Linux is using 64K page granularity, every page will be slipt in multiple non-contiguous 4K MFN (page granularity of Xen).
But you don't care about that on the Linux layer I think? As in, is there an SWIOTLB that does PFN to MFN and vice-versa translation? I thought that ARM guests are not exposed to the MFN<->PFN logic and trying to figure that out to not screw up the DMA engine on a PCIe device slurping up contingous MFNs which don't map to contingous PFNs?
quoted hunk ↗ jump to hunk
I'm not sure how to handle efficiently the check to know whether we can merge 2 biovec with a such case. So for now, always says that biovec are not mergeable. Signed-off-by: Julien Grall <redacted> Cc: Konrad Rzeszutek Wilk <redacted> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <redacted> --- Changes in v2: - Remove the workaround and check if the Linux page granularity is the same as Xen or not --- drivers/xen/biomerge.c | 7 +++++++ 1 file changed, 7 insertions(+)diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c index 0edb91c..571567c 100644 --- a/drivers/xen/biomerge.c +++ b/drivers/xen/biomerge.c@@ -6,10 +6,17 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, const struct bio_vec *vec2) { +#if XEN_PAGE_SIZE == PAGE_SIZE unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page)); unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page)); return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && ((mfn1 == mfn2) || ((mfn1+1) == mfn2)); +#else + /* XXX: bio_vec are not mergeable when using different page size in + * Xen and Linux + */ + return 0; +#endif } EXPORT_SYMBOL(xen_biovec_phys_mergeable);-- 2.1.4