xen/pvh: MMU changes for PVH (v2)

.. which are surprisingly small compared to the amount for PV code.

PVH uses mostly native mmu ops, we leave the generic (native_*) for
the majority and just overwrite the baremetal with the ones we need.

At startup, we are running with pre-allocated page-tables
courtesy of the tool-stack. But we still need to graft them
in the Linux initial pagetables. However there is no need to
unpin/pin and change them to R/O or R/W.

Note that the xen_pagetable_init due to 7836fec9d0994cc9c9150c5a33f0eb0eb08a335a
"xen/mmu/p2m: Refactor the xen_pagetable_init code." does not
need any changes - we just need to make sure that xen_post_allocator_init
does not alter the pvops from the default native one.
Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

arch/x86/xen/mmu.c

@@ -1757,6 +1757,10 @@ static void set_page_prot_flags(void *addr, pgprot_t prot, unsigned long flags)
 	unsigned long pfn = __pa(addr) >> PAGE_SHIFT;
 	pte_t pte = pfn_pte(pfn, prot);
 
+	/* For PVH no need to set R/O or R/W to pin them or unpin them. */
+	if (xen_feature(XENFEAT_auto_translated_physmap))
+		return;
+
 	if (HYPERVISOR_update_va_mapping((unsigned long)addr, pte, flags))
 		BUG();
 }
@@ -1867,6 +1871,7 @@ static void __init check_pt_base(unsigned long *pt_base, unsigned long *pt_end,
  * but that's enough to get __va working.  We need to fill in the rest
  * of the physical mapping once some sort of allocator has been set
  * up.
+ * NOTE: for PVH, the page tables are native.
  */
 void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 {
@@ -1888,6 +1893,7 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 	/* Zap identity mapping */
 	init_level4_pgt[0] = __pgd(0);
 
+	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 		/* Pre-constructed entries are in pfn, so convert to mfn */
 		/* L4[272] -> level3_ident_pgt
 		 * L4[511] -> level3_kernel_pgt */
@@ -1898,7 +1904,7 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 		/* L3_k[510] -> level2_kernel_pgt
 		 * L3_i[511] -> level2_fixmap_pgt */
 		convert_pfn_mfn(level3_kernel_pgt);
-
+	}
 	/* We get [511][511] and have Xen's version of level2_kernel_pgt */
 	l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd);
 	l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud);
@@ -1922,7 +1928,7 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 	copy_page(level2_fixmap_pgt, l2);
 	/* Note that we don't do anything with level1_fixmap_pgt which
 	 * we don't need. */
-
+	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 		/* Make pagetable pieces RO */
 		set_page_prot(init_level4_pgt, PAGE_KERNEL_RO);
 		set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
@@ -1947,6 +1953,8 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 		xen_mc_batch();
 		__xen_write_cr3(true, __pa(init_level4_pgt));
 		xen_mc_issue(PARAVIRT_LAZY_CPU);
+	} else
+		native_write_cr3(__pa(init_level4_pgt));
 
 	/* We can't that easily rip out L3 and L2, as the Xen pagetables are
 	 * set out this way: [L4], [L1], [L2], [L3], [L1], [L1] ...  for
@@ -2107,6 +2115,9 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 
 static void __init xen_post_allocator_init(void)
 {
+	if (xen_feature(XENFEAT_auto_translated_physmap))
+		return;
+
 	pv_mmu_ops.set_pte = xen_set_pte;
 	pv_mmu_ops.set_pmd = xen_set_pmd;
 	pv_mmu_ops.set_pud = xen_set_pud;