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Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features



Hi Paul,

On 04/08/2020 08:49, Paul Durrant wrote:
diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index 931404c..b5fc066 100644
--- a/tools/libxc/xc_dom_arm.c
+++ b/tools/libxc/xc_dom_arm.c
@@ -26,11 +26,19 @@
  #include "xg_private.h"
  #include "xc_dom.h"

-#define NR_MAGIC_PAGES 4
+
  #define CONSOLE_PFN_OFFSET 0
  #define XENSTORE_PFN_OFFSET 1
  #define MEMACCESS_PFN_OFFSET 2
  #define VUART_PFN_OFFSET 3
+#define IOREQ_SERVER_PFN_OFFSET 4
+
+#define NR_IOREQ_SERVER_PAGES 8
+#define NR_MAGIC_PAGES (4 + NR_IOREQ_SERVER_PAGES)
+
+#define GUEST_MAGIC_BASE_PFN (GUEST_MAGIC_BASE >> XC_PAGE_SHIFT)
+
+#define special_pfn(x)  (GUEST_MAGIC_BASE_PFN + (x))

Why introduce 'magic pages' for Arm? It's quite a horrible hack that we have 
begun to do away with by adding resource mapping.

This would require us to mandate at least Linux 4.17 in a domain that will run an IOREQ server. If we don't mandate this, the minimum version would be 4.10 where DM OP was introduced.

Because of XSA-300, we could technically not safely run an IOREQ server with existing Linux. So it is probably OK to enforce the use of the acquire interface.

Note that I haven't yet looked at the rest of the series. So I am not sure if there is more work necessary to enable it.

Cheers,

--
Julien Grall



 


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