From e68266b7001a4e29af083716f0c36c0d6dbb1b39 Mon Sep 17 00:00:00 2001 From: Ian Campbell Date: Wed, 13 Jan 2010 10:16:08 +0000 Subject: [PATCH] x86: xen: 64-bit kernel RPL should be 0 Under Xen 64 bit guests actually run their kernel in ring 3, however the hypervisor takes care of squashing descriptor the RPLs transparently (in order to allow them to continue to differentiate between user and kernel space CS using the RPL). Therefore the Xen paravirt backend should use RPL==0 instead of 1 (or 3). Using RPL==1 causes generic arch code to take incorrect code paths because it uses "testl $3, , je foo" type tests for a userspace CS and this considers 1==userspace. This issue was previously masked because get_kernel_rpl() was omitted when setting CS in kernel_thread(). This was fixed when kernel_thread() was unified with 32 bit in f443ff4201dd25cd4dec183f9919ecba90c8edc2. Signed-off-by: Ian Campbell Cc: Christian Kujau Cc: Jeremy Fitzhardinge Cc: Cyrill Gorcunov Cc: Brian Gerst LKML-Reference: <1263377768-19600-2-git-send-email-ian.campbell@citrix.com> Signed-off-by: Ingo Molnar --- arch/x86/xen/enlighten.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 2b26dd5930c6..36daccb68642 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1151,9 +1151,13 @@ asmlinkage void __init xen_start_kernel(void) /* keep using Xen gdt for now; no urgent need to change it */ +#ifdef CONFIG_X86_32 pv_info.kernel_rpl = 1; if (xen_feature(XENFEAT_supervisor_mode_kernel)) pv_info.kernel_rpl = 0; +#else + pv_info.kernel_rpl = 0; +#endif /* set the limit of our address space */ xen_reserve_top();