On 11/26/2014, 09:56 PM, Chris J Arges wrote:
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> 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.
Now applied to 3.12. Thanks.
> Reported-by: Chris Webb <chris@xxxxxxxxxxxx>
> Tested-by: Chris Webb <chris@xxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Acked-by: Borislav Petkov <bp@xxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> (cherry picked from commit c1118b3602c2329671ad5ec8bdf8e374323d6343)
> Signed-off-by: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
>
> Conflicts:
> arch/x86/include/asm/cpufeature.h
> ---
> 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(-)
>
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 89270b4..c2f19a8 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -203,6 +203,7 @@
> #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 c7678e4..e62cf89 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -2,6 +2,7 @@
> #define _ASM_X86_KVM_PARA_H
>
> #include <asm/processor.h>
> +#include <asm/alternative.h>
> #include <uapi/asm/kvm_para.h>
>
> extern void kvmclock_init(void);
> @@ -16,10 +17,15 @@ static inline bool kvm_check_and_clear_guest_paused(void)
> }
> #endif /* CONFIG_KVM_GUEST */
>
> -/* 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 vmcall or the vmmcall
> * 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 28233b9..ee51e67 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;
>
--
js
suse labs
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