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Thomas Gleixner 55d9115831 x86/speculation/mds: Add mitigation mode VMWERV 
commit 22dd836508 upstream.

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 VMWERV 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 <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jon Masters <jcm@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
History 2019-05-22 23:15:24 +01:00
..
asm x86/speculation/mds: Add mitigation mode VMWERV 2019-05-22 23:15:24 +01:00
uapi/asm x86/speculation/mds: Add basic bug infrastructure for MDS 2019-05-22 23:15:20 +01:00