From 9a8d305befe3218c7523179c0d406d876b5cbbed Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 22 Sep 2014 13:17:48 +0200 Subject: x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only commit c1118b3602c2329671ad5ec8bdf8e374323d6343 upstream. On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. In that case, KVM will fail to patch VMCALL instructions to VMMCALL as required on AMD processors. The failure mode is currently a divide-by-zero exception, which obviously is a KVM bug that has to be fixed. However, picking the right instruction between VMCALL and VMMCALL will be faster and will help if you cannot upgrade the hypervisor. Reported-by: Chris Webb Tested-by: Chris Webb Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Acked-by: Borislav Petkov Signed-off-by: Paolo Bonzini [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- arch/x86/kernel/cpu/amd.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'arch/x86/kernel/cpu/amd.c') diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index f07becc715bb..2d44a28be0ea 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -469,6 +469,13 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c) set_cpu_cap(c, X86_FEATURE_EXTD_APICID); } #endif + + /* + * This is only needed to tell the kernel whether to use VMCALL + * and VMMCALL. VMMCALL is never executed except under virt, so + * we can set it unconditionally. + */ + set_cpu_cap(c, X86_FEATURE_VMMCALL); } static void __cpuinit init_amd(struct cpuinfo_x86 *c) -- cgit v1.2.3