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 | |
| 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>
| -rw-r--r-- | arch/x86/include/asm/cpufeature.h | 1 | ||||
| -rw-r--r-- | arch/x86/include/asm/kvm_para.h | 10 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/amd.c | 7 |
3 files changed, 16 insertions, 2 deletions
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index a315f1ccbf93..b8a5fe545f95 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -193,6 +193,7 @@ #define X86_FEATURE_DECODEASSISTS (8*32+12) /* AMD Decode Assists support */ #define X86_FEATURE_PAUSEFILTER (8*32+13) /* AMD filtered pause intercept */ #define X86_FEATURE_PFTHRESHOLD (8*32+14) /* AMD pause filter threshold */ +#define X86_FEATURE_VMMCALL ( 8*32+15) /* Prefer vmmcall to vmcall */ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */ diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h index 734c3767cfac..9f0a680a7e12 100644 --- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -91,15 +91,21 @@ struct kvm_vcpu_pv_apf_data { #ifdef __KERNEL__ #include <asm/processor.h> +#include <asm/alternative.h> extern void kvmclock_init(void); extern int kvm_register_clock(char *txt); -/* This instruction is vmcall. On non-VT architectures, it will generate a - * trap that we will then rewrite to the appropriate instruction. +#ifdef CONFIG_DEBUG_RODATA +#define KVM_HYPERCALL \ + ALTERNATIVE(".byte 0x0f,0x01,0xc1", ".byte 0x0f,0x01,0xd9", X86_FEATURE_VMMCALL) +#else +/* On AMD processors, vmcall will generate a trap that we will + * then rewrite to the appropriate instruction. */ #define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1" +#endif /* For KVM hypercalls, a three-byte sequence of either the vmrun or the vmmrun * instruction. The hypervisor may replace it with something else but only the 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) |