From 318f5a2a672152328c9fb4dead504b89ec738a43 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 3 Aug 2011 09:31:53 -0400 Subject: x86-64: Add user_64bit_mode paravirt op Three places in the kernel assume that the only long mode CPL 3 selector is __USER_CS. This is not true on Xen -- Xen's sysretq changes cs to the magic value 0xe033. Two of the places are corner cases, but as of "x86-64: Improve vsyscall emulation CS and RIP handling" (c9712944b2a12373cb6ff8059afcfb7e826a6c54), vsyscalls will segfault if called with Xen's extra CS selector. This causes a panic when older init builds die. It seems impossible to make Xen use __USER_CS reliably without taking a performance hit on every system call, so this fixes the tests instead with a new paravirt op. It's a little ugly because ptrace.h can't include paravirt.h. Signed-off-by: Andy Lutomirski Link: http://lkml.kernel.org/r/f4fcb3947340d9e96ce1054a432f183f9da9db83.1312378163.git.luto@mit.edu Reported-by: Konrad Rzeszutek Wilk Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/desc.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/include/asm/desc.h') diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index 7b439d9aea2a..41935fadfdfc 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -27,8 +27,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in desc->base2 = (info->base_addr & 0xff000000) >> 24; /* - * Don't allow setting of the lm bit. It is useless anyway - * because 64bit system calls require __USER_CS: + * Don't allow setting of the lm bit. It would confuse + * user_64bit_mode and would get overridden by sysret anyway. */ desc->l = 0; } -- cgit v1.2.2