x86_64,vsyscall: Make vsyscall emulation configurable
This adds CONFIG_X86_VSYSCALL_EMULATION, guarded by CONFIG_EXPERT.
Turning it off completely disables vsyscall emulation, saving ~3.5k
for vsyscall_64.c, 4k for vsyscall_emu_64.S (the fake vsyscall
page), some tiny amount of core mm code that supports a gate area,
and possibly 4k for a wasted pagetable. The latter is because the
vsyscall addresses are misaligned and fit poorly in the fixmap.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Link: http://lkml.kernel.org/r/406db88b8dd5f0cbbf38216d11be34bbb43c7eae.1414618407.git.luto@amacapital.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index a8a1a3d..8906cf0 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1457,8 +1457,10 @@
page->private = (unsigned long)user_pgd;
if (user_pgd != NULL) {
+#ifdef CONFIG_X86_VSYSCALL_EMULATION
user_pgd[pgd_index(VSYSCALL_ADDR)] =
__pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
+#endif
ret = 0;
}
@@ -2021,7 +2023,7 @@
# ifdef CONFIG_HIGHMEM
case FIX_KMAP_BEGIN ... FIX_KMAP_END:
# endif
-#else
+#elif defined(CONFIG_X86_VSYSCALL_EMULATION)
case VSYSCALL_PAGE:
#endif
case FIX_TEXT_POKE0:
@@ -2060,7 +2062,7 @@
__native_set_fixmap(idx, pte);
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_VSYSCALL_EMULATION
/* Replicate changes to map the vsyscall page into the user
pagetable vsyscall mapping. */
if (idx == VSYSCALL_PAGE) {