[MODERATED] Re: [patch V4 09/11] x86/speculation/mds: Add mitigation mode VMWERV

On Fri, Feb 22, 2019 at 11:24:27PM +0100, speck for Thomas Gleixner wrote:
> From: Thomas Gleixner <[email protected]>
> 
> In virtualized environments it can happen that the host has the microcode
> update which utilizes the VERW instruction to clear CPU buffers, but the
> hypervisor is not yet updated to expose the X86_FEATURE_MD_CLEAR CPUID bit
> to guests.
> 
> Introduce an internal mitigation mode VWWERV which enables the invocation
> of the CPU buffer clearing even if X86_FEATURE_MD_CLEAR is not set. If the
> system has no updated microcode this results in a pointless execution of
> the VERW instruction wasting a few CPU cycles. If the microcode is updated,
> but not exposed to a guest then the CPU buffers will be cleared.
> 
> That said: Virtual Machines Will Eventually Receive Vaccine
> 
> Signed-off-by: Thomas Gleixner <[email protected]>

Thanks for the documentation update here, looks good.

Reviewed-by: Greg Kroah-Hartman <[email protected]>