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authorAndy Lutomirski <luto@MIT.EDU>2011-08-03 09:31:53 -0400
committerH. Peter Anvin <hpa@linux.intel.com>2011-08-04 16:13:49 -0700
commit318f5a2a672152328c9fb4dead504b89ec738a43 (patch)
treed37bcc93c8c1b29c057c44dac13148531706631e /arch/x86/include/asm/desc.h
parent5d5791af4c0d4fd32093882357506355c3357503 (diff)
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 <luto@mit.edu> Link: http://lkml.kernel.org/r/f4fcb3947340d9e96ce1054a432f183f9da9db83.1312378163.git.luto@mit.edu Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include/asm/desc.h')
-rw-r--r--arch/x86/include/asm/desc.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 7b439d9aea2..41935fadfdf 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;
}