Re: [patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use

[Konrad Rzeszutek Wilk]

On Sun, Nov 25, 2018 at 07:33:33PM +0100, Thomas Gleixner wrote:
> If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
> user space exploits from hyperthread sibling.
> 
> Disable STIBP when enhanced IBRS is used.
Reviewed-by: Konrad Rzeszutek Wilk 

Thank you!
> 
> Signed-off-by: Tim Chen 
> Signed-off-by: Thomas Gleixner 
> 
> ---
>  arch/x86/kernel/cpu/bugs.c |7 +++
>  1 file changed, 7 insertions(+)
> 
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -321,6 +321,10 @@ static bool stibp_needed(void)
>   if (spectre_v2_enabled == SPECTRE_V2_NONE)
>   return false;
>  
> + /* Enhanced IBRS makes using STIBP unnecessary. */
> + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> + return false;
> +
>   if (!boot_cpu_has(X86_FEATURE_STIBP))
>   return false;
>  
> @@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf
>  
>  static char *stibp_state(void)
>  {
> + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> + return "";
> +
>   if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
>   return ", STIBP";
>   else
> 
> 

Re: [patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use

[Konrad Rzeszutek Wilk]

On Sun, Nov 25, 2018 at 07:33:33PM +0100, Thomas Gleixner wrote:
> If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
> user space exploits from hyperthread sibling.
> 
> Disable STIBP when enhanced IBRS is used.
Reviewed-by: Konrad Rzeszutek Wilk 

Thank you!
> 
> Signed-off-by: Tim Chen 
> Signed-off-by: Thomas Gleixner 
> 
> ---
>  arch/x86/kernel/cpu/bugs.c |7 +++
>  1 file changed, 7 insertions(+)
> 
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -321,6 +321,10 @@ static bool stibp_needed(void)
>   if (spectre_v2_enabled == SPECTRE_V2_NONE)
>   return false;
>  
> + /* Enhanced IBRS makes using STIBP unnecessary. */
> + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> + return false;
> +
>   if (!boot_cpu_has(X86_FEATURE_STIBP))
>   return false;
>  
> @@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf
>  
>  static char *stibp_state(void)
>  {
> + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> + return "";
> +
>   if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
>   return ", STIBP";
>   else
> 
> 

[patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use

[Thomas Gleixner]

If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
user space exploits from hyperthread sibling.

Disable STIBP when enhanced IBRS is used.

Signed-off-by: Tim Chen 
Signed-off-by: Thomas Gleixner 

---
 arch/x86/kernel/cpu/bugs.c |7 +++
 1 file changed, 7 insertions(+)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -321,6 +321,10 @@ static bool stibp_needed(void)
if (spectre_v2_enabled == SPECTRE_V2_NONE)
return false;
 
+   /* Enhanced IBRS makes using STIBP unnecessary. */
+   if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+   return false;
+
if (!boot_cpu_has(X86_FEATURE_STIBP))
return false;
 
@@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf
 
 static char *stibp_state(void)
 {
+   if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+   return "";
+
if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
return ", STIBP";
else

[patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use

[Thomas Gleixner]

If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
user space exploits from hyperthread sibling.

Disable STIBP when enhanced IBRS is used.

Signed-off-by: Tim Chen 
Signed-off-by: Thomas Gleixner 

---
 arch/x86/kernel/cpu/bugs.c |7 +++
 1 file changed, 7 insertions(+)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -321,6 +321,10 @@ static bool stibp_needed(void)
if (spectre_v2_enabled == SPECTRE_V2_NONE)
return false;
 
+   /* Enhanced IBRS makes using STIBP unnecessary. */
+   if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+   return false;
+
if (!boot_cpu_has(X86_FEATURE_STIBP))
return false;
 
@@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf
 
 static char *stibp_state(void)
 {
+   if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+   return "";
+
if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
return ", STIBP";
else