Re: [PATCH] x86/vmx: correct the SMEP logic for HVM_CR0_GUEST_RESERVED_BITS

Re: [PATCH] x86/vmx: correct the SMEP logic for HVM_CR0_GUEST_RESERVED_BITS

[Andrew Cooper]

On 23/04/14 15:32, Feng Wu wrote:
> When checking the SMEP feature for HVM guests, we should check the
> VCPU instead of the host CPU.
>
> Signed-off-by: Feng Wu <feng.wu@intel.com>
> ---
>  xen/include/asm-x86/hvm/hvm.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
> index dcc3483..74a09ef 100644
> --- a/xen/include/asm-x86/hvm/hvm.h
> +++ b/xen/include/asm-x86/hvm/hvm.h
> @@ -351,6 +351,15 @@ static inline int hvm_event_pending(struct vcpu *v)
>      return hvm_funcs.event_pending(v);
>  }
>  
> +static inline bool_t hvm_vcpu_has_smep(void)
> +{
> +    unsigned int ebx = 0, leaf = 0x7;

You need to check hvm_cpuid.0.eax for max leaf.

~Andrew

> +
> +    hvm_cpuid(leaf, NULL, &ebx, NULL, NULL);
> +
> +    return !!(ebx & cpufeat_mask(X86_FEATURE_SMEP));
> +}
> +
>  /* These reserved bits in lower 32 remain 0 after any load of CR0 */
>  #define HVM_CR0_GUEST_RESERVED_BITS             \
>      (~((unsigned long)                          \
> @@ -370,7 +379,7 @@ static inline int hvm_event_pending(struct vcpu *v)
>          X86_CR4_DE  | X86_CR4_PSE | X86_CR4_PAE |       \
>          X86_CR4_MCE | X86_CR4_PGE | X86_CR4_PCE |       \
>          X86_CR4_OSFXSR | X86_CR4_OSXMMEXCPT |           \
> -        (cpu_has_smep ? X86_CR4_SMEP : 0) |             \
> +        (hvm_vcpu_has_smep() ? X86_CR4_SMEP : 0) |      \
>          (cpu_has_fsgsbase ? X86_CR4_FSGSBASE : 0) |     \
>          ((nestedhvm_enabled((_v)->domain) && cpu_has_vmx)\
>                        ? X86_CR4_VMXE : 0)  |             \

Re: [PATCH] x86/vmx: correct the SMEP logic for HVM_CR0_GUEST_RESERVED_BITS

[Jan Beulich]

>>> On 23.04.14 at 16:32, <feng.wu@intel.com> wrote:
> --- a/xen/include/asm-x86/hvm/hvm.h
> +++ b/xen/include/asm-x86/hvm/hvm.h
> @@ -351,6 +351,15 @@ static inline int hvm_event_pending(struct vcpu *v)
>      return hvm_funcs.event_pending(v);
>  }
>  
> +static inline bool_t hvm_vcpu_has_smep(void)
> +{
> +    unsigned int ebx = 0, leaf = 0x7;

Pointless initializer for ebx, and pointless variable leaf.

> +    hvm_cpuid(leaf, NULL, &ebx, NULL, NULL);

And, as I just saw Andrew already pointed out, this needs gating on
there being a (visible) leaf 7 in the first place.

Jan

[PATCH] x86/vmx: correct the SMEP logic for HVM_CR0_GUEST_RESERVED_BITS

[Feng Wu]

When checking the SMEP feature for HVM guests, we should check the
VCPU instead of the host CPU.

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
 xen/include/asm-x86/hvm/hvm.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index dcc3483..74a09ef 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -351,6 +351,15 @@ static inline int hvm_event_pending(struct vcpu *v)
     return hvm_funcs.event_pending(v);
 }
 
+static inline bool_t hvm_vcpu_has_smep(void)
+{
+    unsigned int ebx = 0, leaf = 0x7;
+
+    hvm_cpuid(leaf, NULL, &ebx, NULL, NULL);
+
+    return !!(ebx & cpufeat_mask(X86_FEATURE_SMEP));
+}
+
 /* These reserved bits in lower 32 remain 0 after any load of CR0 */
 #define HVM_CR0_GUEST_RESERVED_BITS             \
     (~((unsigned long)                          \
@@ -370,7 +379,7 @@ static inline int hvm_event_pending(struct vcpu *v)
         X86_CR4_DE  | X86_CR4_PSE | X86_CR4_PAE |       \
         X86_CR4_MCE | X86_CR4_PGE | X86_CR4_PCE |       \
         X86_CR4_OSFXSR | X86_CR4_OSXMMEXCPT |           \
-        (cpu_has_smep ? X86_CR4_SMEP : 0) |             \
+        (hvm_vcpu_has_smep() ? X86_CR4_SMEP : 0) |      \
         (cpu_has_fsgsbase ? X86_CR4_FSGSBASE : 0) |     \
         ((nestedhvm_enabled((_v)->domain) && cpu_has_vmx)\
                       ? X86_CR4_VMXE : 0)  |             \
-- 
1.8.3.1