x86/bugs, KVM: Support the combination of guest and host IBRS
authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Thu, 26 Apr 2018 02:04:19 +0000 (22:04 -0400)
committerThomas Gleixner <tglx@linutronix.de>
Thu, 3 May 2018 11:55:47 +0000 (13:55 +0200)
commit5cf687548705412da47c9cec342fd952d71ed3d5
tree5b868ec35064f655e390b04a8ff520af0a660e7e
parent1b86883ccb8d5d9506529d42dbe1a5257cb30b18
x86/bugs, KVM: Support the combination of guest and host IBRS

A guest may modify the SPEC_CTRL MSR from the value used by the
kernel. Since the kernel doesn't use IBRS, this means a value of zero is
what is needed in the host.

But the 336996-Speculative-Execution-Side-Channel-Mitigations.pdf refers to
the other bits as reserved so the kernel should respect the boot time
SPEC_CTRL value and use that.

This allows to deal with future extensions to the SPEC_CTRL interface if
any at all.

Note: This uses wrmsrl() instead of native_wrmsl(). I does not make any
difference as paravirt will over-write the callq *0xfff.. with the wrmsrl
assembler code.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
arch/x86/include/asm/nospec-branch.h
arch/x86/kernel/cpu/bugs.c
arch/x86/kvm/svm.c
arch/x86/kvm/vmx.c