[PATCH v2] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[PATCH v2] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[Abhishek Bhardwaj]

This change adds a new kernel configuration that sets the l1d cache
flush setting at compile time rather than at run time.

Signed-off-by: Abhishek Bhardwaj <abhishekbh@google.com>

---

Changes in v2:
- Fix typo in the help of the new KConfig.

 arch/x86/kernel/cpu/bugs.c |  8 ++++++++
 arch/x86/kvm/Kconfig       | 17 +++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b71970d2d3d2..1dcc875cf5547 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1406,7 +1406,15 @@ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
 #if IS_ENABLED(CONFIG_KVM_INTEL)
 EXPORT_SYMBOL_GPL(l1tf_mitigation);
 #endif
+#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NEVER;
+#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_COND;
+#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_ALWAYS;
+#else
 enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
+#endif
 EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
 
 /*
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index b277a2db62676..d375dcedd447d 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -107,4 +107,21 @@ config KVM_MMU_AUDIT
 	 This option adds a R/W kVM module parameter 'mmu_audit', which allows
 	 auditing of KVM MMU events at runtime.
 
+config KVM_VMENTRY_L1D_FLUSH
+	int "L1D cache flush settings (1-3)"
+	range 1 3
+	default "2"
+	depends on KVM && X86 && X86_64
+	help
+	 This setting determines the L1D cache flush behavior before a VMENTER.
+	 This is similar to setting the option / parameter to
+	 kvm-intel.vmentry_l1d_flush.
+	 1 - Never flush.
+	 2 - Conditionally flush.
+	 3 - Always flush.
+
+# OK, it's a little counter-intuitive to do this, but it puts it neatly under
+# the virtualization menu.
+source "drivers/vhost/Kconfig"
+
 endif # VIRTUALIZATION
-- 
2.27.0.212.ge8ba1cc988-goog

Re: [PATCH v2] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[Randy Dunlap]

Hi--

On 7/2/20 2:38 PM, Abhishek Bhardwaj wrote:
> This change adds a new kernel configuration that sets the l1d cache
> flush setting at compile time rather than at run time.
> 
> Signed-off-by: Abhishek Bhardwaj <abhishekbh@google.com>
> 
> ---
> 
> Changes in v2:
> - Fix typo in the help of the new KConfig.
> 
>  arch/x86/kernel/cpu/bugs.c |  8 ++++++++
>  arch/x86/kvm/Kconfig       | 17 +++++++++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 0b71970d2d3d2..1dcc875cf5547 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1406,7 +1406,15 @@ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
>  #if IS_ENABLED(CONFIG_KVM_INTEL)
>  EXPORT_SYMBOL_GPL(l1tf_mitigation);
>  #endif
> +#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NEVER;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_COND;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_ALWAYS;
> +#else
>  enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
> +#endif
>  EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
>  
>  /*
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index b277a2db62676..d375dcedd447d 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -107,4 +107,21 @@ config KVM_MMU_AUDIT
>  	 This option adds a R/W kVM module parameter 'mmu_audit', which allows
>  	 auditing of KVM MMU events at runtime.
>  
> +config KVM_VMENTRY_L1D_FLUSH
> +	int "L1D cache flush settings (1-3)"
> +	range 1 3
> +	default "2"
> +	depends on KVM && X86 && X86_64

Why does this apply only to KVM?

and the "X86 && X86_64" is more than is needed. Just "X86_64" alone
should be enough.


> +	help
> +	 This setting determines the L1D cache flush behavior before a VMENTER.
> +	 This is similar to setting the option / parameter to
> +	 kvm-intel.vmentry_l1d_flush.
> +	 1 - Never flush.
> +	 2 - Conditionally flush.
> +	 3 - Always flush.
> +
> +# OK, it's a little counter-intuitive to do this, but it puts it neatly under
> +# the virtualization menu.
> +source "drivers/vhost/Kconfig"


I don't quite understand why this 'source' line is here.
Can you explain more about that, please?

It puts "VHOST drivers" in the menu 2 times, in 2 totally unrelated
places.  Seems like it could be confusing.

> +
>  endif # VIRTUALIZATION


-- 
~Randy

Re: [PATCH v2] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[Abhishek Bhardwaj]

On Thu, Jul 2, 2020 at 3:01 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> Hi--
>
> On 7/2/20 2:38 PM, Abhishek Bhardwaj wrote:
> > This change adds a new kernel configuration that sets the l1d cache
> > flush setting at compile time rather than at run time.
> >
> > Signed-off-by: Abhishek Bhardwaj <abhishekbh@google.com>
> >
> > ---
> >
> > Changes in v2:
> > - Fix typo in the help of the new KConfig.
> >
> >  arch/x86/kernel/cpu/bugs.c |  8 ++++++++
> >  arch/x86/kvm/Kconfig       | 17 +++++++++++++++++
> >  2 files changed, 25 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> > index 0b71970d2d3d2..1dcc875cf5547 100644
> > --- a/arch/x86/kernel/cpu/bugs.c
> > +++ b/arch/x86/kernel/cpu/bugs.c
> > @@ -1406,7 +1406,15 @@ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
> >  #if IS_ENABLED(CONFIG_KVM_INTEL)
> >  EXPORT_SYMBOL_GPL(l1tf_mitigation);
> >  #endif
> > +#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
> > +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NEVER;
> > +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
> > +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_COND;
> > +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
> > +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_ALWAYS;
> > +#else
> >  enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
> > +#endif
> >  EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
> >
> >  /*
> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index b277a2db62676..d375dcedd447d 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -107,4 +107,21 @@ config KVM_MMU_AUDIT
> >        This option adds a R/W kVM module parameter 'mmu_audit', which allows
> >        auditing of KVM MMU events at runtime.
> >
> > +config KVM_VMENTRY_L1D_FLUSH
> > +     int "L1D cache flush settings (1-3)"
> > +     range 1 3
> > +     default "2"
> > +     depends on KVM && X86 && X86_64
>
> Why does this apply only to KVM?
Sorry, I don't know what this means. The runtime options this aims to
emulate applied to kvm driver.
Hence, this kernel config applies to KVM ?

>
> and the "X86 && X86_64" is more than is needed. Just "X86_64" alone
> should be enough.
Fixed in v3.

>
>
> > +     help
> > +      This setting determines the L1D cache flush behavior before a VMENTER.
> > +      This is similar to setting the option / parameter to
> > +      kvm-intel.vmentry_l1d_flush.
> > +      1 - Never flush.
> > +      2 - Conditionally flush.
> > +      3 - Always flush.
> > +
> > +# OK, it's a little counter-intuitive to do this, but it puts it neatly under
> > +# the virtualization menu.
> > +source "drivers/vhost/Kconfig"
This was a bad copy paste. Removed in v3.
>
>
> I don't quite understand why this 'source' line is here.
> Can you explain more about that, please?
>
> It puts "VHOST drivers" in the menu 2 times, in 2 totally unrelated
> places.  Seems like it could be confusing.
>
> > +
> >  endif # VIRTUALIZATION
>
>
> --
> ~Randy
>


-- 
Abhishek

Re: [PATCH v2] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[Xiaoyao Li]

On 7/3/2020 5:38 AM, Abhishek Bhardwaj wrote:
> This change adds a new kernel configuration that sets the l1d cache
> flush setting at compile time rather than at run time.
> 
> Signed-off-by: Abhishek Bhardwaj <abhishekbh@google.com>
> 
> ---
> 
> Changes in v2:
> - Fix typo in the help of the new KConfig.
> 
>   arch/x86/kernel/cpu/bugs.c |  8 ++++++++
>   arch/x86/kvm/Kconfig       | 17 +++++++++++++++++
>   2 files changed, 25 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 0b71970d2d3d2..1dcc875cf5547 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1406,7 +1406,15 @@ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
>   #if IS_ENABLED(CONFIG_KVM_INTEL)
>   EXPORT_SYMBOL_GPL(l1tf_mitigation);
>   #endif
> +#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NEVER;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_COND;
> +#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
> +enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_ALWAYS;
> +#else
>   enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
> +#endif

how about

enum vmx_l1d_flush_state l1tf_vmx_mitigation =
#if (CONFIG_KVM_VMENTRY_L1D_FLUSH == 1)
	VMENTER_L1D_FLUSH_NEVER;
#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 2)
	VMENTER_L1D_FLUSH_COND;
#elif (CONFIG_KVM_VMENTRY_L1D_FLUSH == 3)
	VMENTER_L1D_FLUSH_ALWAYS;
#else
	VMENTER_L1D_FLUSH_AUTO;
#endif