[PATCHv6 17/19] x86/xen: Allow XEN_PV and XEN_PVH to be enabled with X86_5LEVEL

[Kirill A. Shutemov]

With boot-time switching between paging modes, XEN_PV and XEN_PVH can be
boot into 4-level paging mode.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Tested-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/kernel/head_64.S | 12 ++++++------
 arch/x86/xen/Kconfig      |  5 -----
 arch/x86/xen/mmu_pv.c     | 21 +++++++++++++++++++++
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 49f8bb43d107..e137f2665fc2 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -37,12 +37,12 @@
  *
  */
 
+#define l4_index(x)	(((x) >> 39) & 511)
 #define pud_index(x)	(((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
 
-#if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
-PGD_PAGE_OFFSET = pgd_index(__PAGE_OFFSET_BASE48)
-PGD_START_KERNEL = pgd_index(__START_KERNEL_map)
-#endif
+L4_PAGE_OFFSET = l4_index(__PAGE_OFFSET_BASE48)
+L4_START_KERNEL = l4_index(__START_KERNEL_map)
+
 L3_START_KERNEL = pud_index(__START_KERNEL_map)
 
 	.text
@@ -363,9 +363,9 @@ NEXT_PAGE(early_dynamic_pgts)
 #if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
 NEXT_PAGE(init_top_pgt)
 	.quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
-	.org    init_top_pgt + PGD_PAGE_OFFSET*8, 0
+	.org    init_top_pgt + L4_PAGE_OFFSET*8, 0
 	.quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
-	.org    init_top_pgt + PGD_START_KERNEL*8, 0
+	.org    init_top_pgt + L4_START_KERNEL*8, 0
 	/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
 	.quad   level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
 
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 1ecd419811a2..027987638e98 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -17,9 +17,6 @@ config XEN_PV
 	bool "Xen PV guest support"
 	default y
 	depends on XEN
-	# XEN_PV is not ready to work with 5-level paging.
-	# Changes to hypervisor are also required.
-	depends on !X86_5LEVEL
 	select XEN_HAVE_PVMMU
 	select XEN_HAVE_VPMU
 	help
@@ -78,6 +75,4 @@ config XEN_DEBUG_FS
 config XEN_PVH
 	bool "Support for running as a PVH guest"
 	depends on XEN && XEN_PVHVM && ACPI
-	# Pre-built page tables are not ready to handle 5-level paging.
-	depends on !X86_5LEVEL
 	def_bool n
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index bc5fddd64217..55b529c36f16 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -558,6 +558,22 @@ static void xen_set_p4d(p4d_t *ptr, p4d_t val)
 
 	xen_mc_issue(PARAVIRT_LAZY_MMU);
 }
+
+#if CONFIG_PGTABLE_LEVELS >= 5
+__visible p4dval_t xen_p4d_val(p4d_t p4d)
+{
+	return pte_mfn_to_pfn(p4d.p4d);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_p4d_val);
+
+__visible p4d_t xen_make_p4d(p4dval_t p4d)
+{
+	p4d = pte_pfn_to_mfn(p4d);
+
+	return native_make_p4d(p4d);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_make_p4d);
+#endif  /* CONFIG_PGTABLE_LEVELS >= 5 */
 #endif	/* CONFIG_X86_64 */
 
 static int xen_pmd_walk(struct mm_struct *mm, pmd_t *pmd,
@@ -2430,6 +2446,11 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {
 
 	.alloc_pud = xen_alloc_pmd_init,
 	.release_pud = xen_release_pmd_init,
+
+#if CONFIG_PGTABLE_LEVELS >= 5
+	.p4d_val = PV_CALLEE_SAVE(xen_p4d_val),
+	.make_p4d = PV_CALLEE_SAVE(xen_make_p4d),
+#endif
 #endif	/* CONFIG_X86_64 */
 
 	.activate_mm = xen_activate_mm,
-- 
2.14.1