diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2014-11-26 14:56:31 -0600 |
|---|---|---|
| committer | Jiri Slaby <jslaby@suse.cz> | 2014-12-03 12:07:27 +0100 |
| commit | a05916f8ff7280e8539dac505bc3100212a3a098 (patch) | |
| tree | aca83a2fb909029adee22b2392c3f8b1f5baac61 /arch/x86/kernel/cpu/amd.c | |
| parent | 7e3bea443c47e2f499d7547dbabafbaacfa2f8e6 (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>
Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
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 28233b9e45cc..ee51e67df1b1 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -509,6 +509,13 @@ static void early_init_amd(struct cpuinfo_x86 *c) } #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); + /* F16h erratum 793, CVE-2013-6885 */ if (c->x86 == 0x16 && c->x86_model <= 0xf) { u64 val; |