diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2014-09-22 13:17:48 +0200 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2015-01-01 01:27:52 +0000 |
| commit | 9a8d305befe3218c7523179c0d406d876b5cbbed (patch) | |
| tree | 08335ef29b1e35ce33207cefb83d255e43d01f42 /arch/x86/kernel/cpu/amd.c | |
| parent | 85c3fe917f5459427c4ba5797332f9910400afeb (diff) | |
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 <chris@arachsys.com>
Tested-by: Chris Webb <chris@arachsys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'arch/x86/kernel/cpu/amd.c')
| -rw-r--r-- | arch/x86/kernel/cpu/amd.c | 7 |
1 files changed, 7 insertions, 0 deletions
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) |