| From: Paolo Bonzini <pbonzini@redhat.com> |
| 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 <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> |
| --- |
| arch/x86/include/asm/cpufeature.h | 1 + |
| arch/x86/include/asm/kvm_para.h | 10 ++++++++-- |
| arch/x86/kernel/cpu/amd.c | 7 +++++++ |
| 3 files changed, 16 insertions(+), 2 deletions(-) |
| |
| --- 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 */ |
| --- 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 |
| --- a/arch/x86/kernel/cpu/amd.c |
| +++ b/arch/x86/kernel/cpu/amd.c |
| @@ -469,6 +469,13 @@ static void __cpuinit early_init_amd(str |
| 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) |
