x86/xen: Allow XEN_PV and XEN_PVH to be enabled with X86_5LEVEL

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

Tested-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180216114948.68868-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 27 insertions, 11 deletions

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 145d7b95ae29..3e9de0fc97de 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -38,12 +38,12 @@
  *
  */
 
+#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_BASE_L4)
-PGD_START_KERNEL = pgd_index(__START_KERNEL_map)
-#endif
+L4_PAGE_OFFSET = l4_index(__PAGE_OFFSET_BASE_L4)
+L4_START_KERNEL = l4_index(__START_KERNEL_map)
+
 L3_START_KERNEL = pud_index(__START_KERNEL_map)
 
         .text
@@ -386,9 +386,9 @@ NEXT_PAGE(early_dynamic_pgts)
 #if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
 NEXT_PGD_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
         .fill   PTI_USER_PGD_FILL,8,0
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index f605825a04ab..c1f98f32c45f 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -18,9 +18,6 @@ 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
@@ -79,6 +76,4 @@ 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 d85076223a69..3f4fec59af09 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -538,6 +538,22 @@ 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,
@@ -2411,6 +2427,11 @@ 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,