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>

2 files changed, 34 insertions, 3 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 724bffbde54d..0679e11d2cf7 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -101,6 +101,11 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
 	unsigned long mfn;
 
+	/*
+	 * Some x86 code are still using pfn_to_mfn instead of
+	 * pfn_to_mfn. This will have to be removed when we figured
+	 * out which call.
+	 */
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return pfn;
 
@@ -147,6 +152,11 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
 {
 	unsigned long pfn;
 
+	/*
+	 * Some x86 code are still using mfn_to_pfn instead of
+	 * gfn_to_pfn. This will have to be removed when we figure
+	 * out which call.
+	 */
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return mfn;
 
@@ -176,9 +186,26 @@ static inline xpaddr_t machine_to_phys(xmaddr_t machine)
 	return XPADDR(PFN_PHYS(mfn_to_pfn(PFN_DOWN(machine.maddr))) | offset);
 }
 
+/* Pseudo-physical <-> Guest conversion */
+static inline unsigned long pfn_to_gfn(unsigned long pfn)
+{
+	if (xen_feature(XENFEAT_auto_translated_physmap))
+		return pfn;
+	else
+		return pfn_to_mfn(pfn);
+}
+
+static inline unsigned long gfn_to_pfn(unsigned long gfn)
+{
+	if (xen_feature(XENFEAT_auto_translated_physmap))
+		return gfn;
+	else
+		return mfn_to_pfn(gfn);
+}
+
 /* Pseudo-physical <-> Bus conversion */
-#define pfn_to_bfn(pfn)		pfn_to_mfn(pfn)
-#define bfn_to_pfn(bfn)		mfn_to_pfn(bfn)
+#define pfn_to_bfn(pfn)		pfn_to_gfn(pfn)
+#define bfn_to_pfn(bfn)		gfn_to_pfn(bfn)
 
 /*
  * We detect special mappings in one of two ways:
@@ -219,6 +246,10 @@ static inline unsigned long bfn_to_local_pfn(unsigned long mfn)
 #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(g)		(__va(gfn_to_pfn(g) << PAGE_SHIFT))
+
 static inline unsigned long pte_mfn(pte_t pte)
 {
 	return (pte.pte & PTE_PFN_MASK) >> PAGE_SHIFT;
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 2a9ff7342791..3f4ebf0261f2 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -453,7 +453,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
 	}
 #endif
 	ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
-	ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
+	ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_gfn(swapper_pg_dir));
 	if (HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, ctxt))
 		BUG();