[Xen-devel] [Patch] common/memory: Fix ABI breakage for XENMEM_add_to_physmap

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

  caused by c/s 4be86bb194e25e46b6cbee900601bfee76e8090a

In public/memory.h, struct xen_add_to_physmap has 'space' as an unsigned int,
but struct xen_add_to_physmap_batch has 'space' as a uint16_t.

By defining xenmem_add_to_physmap_one() with space defined as uint16_t, the
now-common xenmem_add_to_physmap() implicitly truncates xatp->space from
unsigned int to uint16_t, which changes the space switch()'d upon.

This wouldn't be noticed with any upstream code (of which I am aware), but was
discovered because of the XenServer support for legacy Windows PV drivers,
which make XENMEM_add_to_physmap hypercalls using spaces with the top bit set.
The current Windows PV drivers don't do this any more, but we 'fix' Xen to
support running VMs with out-of-date tools.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>

---

As this breakage was caused between 4.4-rc1 and -rc2, I request a release ack
for the fix.

This was caught by a compile failure rather than a functional test.  I have
encountered a different compile error which turns out to be a bug in the cross
compiler we are currently using, so I need to fix that before I can
functionally test a 4.4-rc2 based XenServer.  (Which will be a rather better
test of whether the functionality of XENMEM_add_to_physmap is actually still
the same.  If anyone dares look,
https://github.com/xenserver/xen-4.3.pg/blob/master/xen-legacy-win-xenmapspace-quirks.patch
are the hacks required to make the legacy drivers work on modern Xen.)
---
 xen/arch/arm/mm.c    |    2 +-
 xen/arch/x86/mm.c    |    2 +-
 xen/include/xen/mm.h |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 293b6e2..127cce0 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -970,7 +970,7 @@ void share_xen_page_with_privileged_guests(
 
 int xenmem_add_to_physmap_one(
     struct domain *d,
-    uint16_t space,
+    unsigned int space,
     domid_t foreign_domid,
     unsigned long idx,
     xen_pfn_t gpfn)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 32c0473..172c68c 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4522,7 +4522,7 @@ static int handle_iomem_range(unsigned long s, unsigned 
long e, void *p)
 
 int xenmem_add_to_physmap_one(
     struct domain *d,
-    uint16_t space,
+    unsigned int space,
     domid_t foreign_domid,
     unsigned long idx,
     xen_pfn_t gpfn)
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index f90ed74..b183189 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -356,7 +356,7 @@ static inline unsigned int get_order_from_pages(unsigned 
long nr_pages)
 
 void scrub_one_page(struct page_info *);
 
-int xenmem_add_to_physmap_one(struct domain *d, uint16_t space,
+int xenmem_add_to_physmap_one(struct domain *d, unsigned int space,
                               domid_t foreign_domid,
                               unsigned long idx, xen_pfn_t gpfn);
 
-- 
1.7.10.4


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