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    SubjectRe: [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 <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

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