2020-07-02 21:41:36

by Abhishek Bhardwaj

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

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 <[email protected]>

---

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

2020-07-02 22:03:49

by Randy Dunlap

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

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 <[email protected]>
>
> ---
>
> 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

2020-07-02 22:16:24

by Abhishek Bhardwaj

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

On Thu, Jul 2, 2020 at 3:01 PM Randy Dunlap <[email protected]> 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 <[email protected]>
> >
> > ---
> >
> > 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

2020-07-08 06:59:45

by Xiaoyao Li

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

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 <[email protected]>
>
> ---
>
> 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