[PATCH] kvm: x86: SRSO_USER_KERNEL_NO is not synthesized

From: Paolo Bonzini
Date: Tue Feb 04 2025 - 11:14:03 EST


SYNTHESIZED_F() generally is used together with setup_force_cpu_cap(),
i.e. when it makes sense to present the feature even if cpuid does not
have it *and* the VM is not able to see the difference. For example,
it can be used when mitigations on the host automatically protect
the guest as well.

The "SYNTHESIZED_F(SRSO_USER_KERNEL_NO)" line came in as a conflict
resolution between the CPUID overhaul from the KVM tree and support
for the feature in the x86 tree. Using it right now does not hurt,
or make a difference for that matter, because there is no
setup_force_cpu_cap(X86_FEATURE_SRSO_USER_KERNEL_NO). However, it
is a little less future proof in case such a setup_force_cpu_cap()
appears later, for a case where the kernel somehow is not vulnerable
but the guest would have to apply the mitigation.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/cpuid.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2cbb3874ad39..8eb3a88707f2 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1180,7 +1180,7 @@ void kvm_set_cpu_caps(void)
SYNTHESIZED_F(SBPB),
SYNTHESIZED_F(IBPB_BRTYPE),
SYNTHESIZED_F(SRSO_NO),
- SYNTHESIZED_F(SRSO_USER_KERNEL_NO),
+ F(SRSO_USER_KERNEL_NO),
);

kvm_cpu_cap_init(CPUID_8000_0022_EAX,
--
2.43.5