xen: Use correctly the Xen memory terminologies

Based on include/xen/mm.h [1], Linux is mistakenly using MFN when GFN
is meant, I suspect this is because the first support for Xen was for
PV. This resulted in some misimplementation of helpers on ARM and
confused developers about the expected behavior.

For instance, with pfn_to_mfn, we expect to get an MFN based on the name.
Although, if we look at the implementation on x86, it's returning a GFN.

For clarity and avoid new confusion, replace any reference to mfn with
gfn in any helpers used by PV drivers. The x86 code will still keep some
reference of pfn_to_mfn which may be used by all kind of guests
No changes as been made in the hypercall field, even
though they may be invalid, in order to keep the same as the defintion
in xen repo.

Note that page_to_mfn has been renamed to xen_page_to_gfn to avoid a
name to close to the KVM function gfn_to_page.

Take also the opportunity to simplify simple construction such
as pfn_to_mfn(page_to_pfn(page)) into xen_page_to_gfn. More complex clean up
will come in follow-up patches.

[1] http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=e758ed14f390342513405dd766e874934573e6cb

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
index 911d62b4df26..127956353b00 100644
--- a/arch/arm/include/asm/xen/page.h
+++ b/arch/arm/include/asm/xen/page.h
@@ -34,14 +34,15 @@ typedef struct xpaddr {
 unsigned long __pfn_to_mfn(unsigned long pfn);
 extern struct rb_root phys_to_mach;
 
-static inline unsigned long pfn_to_mfn(unsigned long pfn)
+/* Pseudo-physical <-> Guest conversion */
+static inline unsigned long pfn_to_gfn(unsigned long pfn)
 {
 	return pfn;
 }
 
-static inline unsigned long mfn_to_pfn(unsigned long mfn)
+static inline unsigned long gfn_to_pfn(unsigned long gfn)
 {
-	return mfn;
+	return gfn;
 }
 
 /* Pseudo-physical <-> BUS conversion */
@@ -65,9 +66,9 @@ static inline unsigned long bfn_to_pfn(unsigned long bfn)
 
 #define bfn_to_local_pfn(bfn)	bfn_to_pfn(bfn)
 
-/* VIRT <-> MACHINE conversion */
-#define virt_to_mfn(v)		(pfn_to_mfn(virt_to_pfn(v)))
-#define mfn_to_virt(m)		(__va(mfn_to_pfn(m) << PAGE_SHIFT))
+/* VIRT <-> GUEST conversion */
+#define virt_to_gfn(v)		(pfn_to_gfn(virt_to_pfn(v)))
+#define gfn_to_virt(m)		(__va(gfn_to_pfn(m) << PAGE_SHIFT))
 
 /* Only used in PV code. But ARM guests are always HVM. */
 static inline xmaddr_t arbitrary_virt_to_machine(void *vaddr)