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Subject: [PATCH 04/12] swiotlb-xen: ensure to issue well-formed
 XENMEM_exchange requests
From:   Jan Beulich <jbeulich@suse.com>
To:     Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
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        lkml <linux-kernel@vger.kernel.org>,
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While the hypervisor hasn't been enforcing this, we would still better
avoid issuing requests with GFNs not aligned to the requested order.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
I wonder how useful it is to include the alignment in the panic()
message. I further wonder how useful it is to wrap "bytes" in
PAGE_ALIGN(), when it is a multiple of a segment's size anyway (or at
least was supposed to be, prior to "swiotlb-xen: maintain slab count
properly").

--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -231,10 +231,10 @@ retry:
 	/*
 	 * Get IO TLB memory from any location.
 	 */
-	start = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
+	start = memblock_alloc(PAGE_ALIGN(bytes), IO_TLB_SEGSIZE << IO_TLB_SHIFT);
 	if (!start)
-		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
-		      __func__, PAGE_ALIGN(bytes), PAGE_SIZE);
+		panic("%s: Failed to allocate %lu bytes align=%#x\n",
+		      __func__, PAGE_ALIGN(bytes), IO_TLB_SEGSIZE << IO_TLB_SHIFT);
 
 	/*
 	 * And replace that memory with pages under 4GB.