[PATCH RFC 2/4] x86/xen: Pin up to VSYSCALL_ADDR when vsyscall page is out of fixmap area

["Hou Wenlong" <houwenlong.hwl@xxxxxxxxxxxx>]

If the vsyscall page is moved out of the fixmap area, then FIXADDR_TOP
would be below the vsyscall page. Therefore, it should be pinned up to
VSYSCALL_ADDR if vsyscall is enabled.

Suggested-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
---
 arch/x86/xen/mmu_pv.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index c42c60faa3bb..c1f298c31e64 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -587,6 +587,12 @@ static void xen_p4d_walk(struct mm_struct *mm, p4d_t *p4d,
        xen_pud_walk(mm, pud, func, last, limit);
 }
 
+#ifdef CONFIG_X86_VSYSCALL_EMULATION
+#define __KERNEL_MAP_TOP       (VSYSCALL_ADDR + PAGE_SIZE)
+#else
+#define __KERNEL_MAP_TOP       FIXADDR_TOP
+#endif
+
 /*
  * (Yet another) pagetable walker.  This one is intended for pinning a
  * pagetable.  This means that it walks a pagetable and calls the
@@ -594,7 +600,7 @@ static void xen_p4d_walk(struct mm_struct *mm, p4d_t *p4d,
  * at every level.  It walks the entire pagetable, but it only bothers
  * pinning pte pages which are below limit.  In the normal case this
  * will be STACK_TOP_MAX, but at boot we need to pin up to
- * FIXADDR_TOP.
+ * __KERNEL_MAP_TOP.
  *
  * We must skip the Xen hole in the middle of the address space, just after
  * the big x86-64 virtual hole.
@@ -609,7 +615,7 @@ static void __xen_pgd_walk(struct mm_struct *mm, pgd_t *pgd,
 
        /* The limit is the last byte to be touched */
        limit--;
-       BUG_ON(limit >= FIXADDR_TOP);
+       BUG_ON(limit >= __KERNEL_MAP_TOP);
 
        /*
         * 64-bit has a great big hole in the middle of the address
@@ -797,7 +803,7 @@ static void __init xen_after_bootmem(void)
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
        SetPagePinned(virt_to_page(level3_user_vsyscall));
 #endif
-       xen_pgd_walk(&init_mm, xen_mark_pinned, FIXADDR_TOP);
+       xen_pgd_walk(&init_mm, xen_mark_pinned, __KERNEL_MAP_TOP);
 }
 
 static void xen_unpin_page(struct mm_struct *mm, struct page *page,
-- 
2.31.1