On Sun, Dec 29, 2019 at 04:51:06PM +0100, gregkh@linuxfoundation.org wrote:
The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 396d2e878f92ec108e4293f1c77ea3bc90b414ff Mon Sep 17 00:00:00 2001 From: Jim Mattson jmattson@google.com Date: Fri, 13 Dec 2019 16:15:15 -0800 Subject: [PATCH] kvm: x86: Host feature SSBD doesn't imply guest feature SPEC_CTRL_SSBD
The host reports support for the synthetic feature X86_FEATURE_SSBD when any of the three following hardware features are set: CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31] CPUID.80000008H:EBX.AMD_SSBD[bit 24] CPUID.80000008H:EBX.VIRT_SSBD[bit 25]
Either of the first two hardware features implies the existence of the IA32_SPEC_CTRL MSR, but CPUID.80000008H:EBX.VIRT_SSBD[bit 25] does not. Therefore, CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31] should only be set in the guest if CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31] or CPUID.80000008H:EBX.AMD_SSBD[bit 24] is set on the host.
Fixes: 0c54914d0c52a ("KVM: x86: use Intel speculation bugs and features as derived in generic x86 code") Signed-off-by: Jim Mattson jmattson@google.com Reviewed-by: Jacob Xu jacobhxu@google.com Reviewed-by: Peter Shier pshier@google.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: stable@vger.kernel.org Reported-by: Eric Biggers ebiggers@kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com
I don't think that this is needed on 4.19 and older, but it would be nice if someone would ack.