From e88cfd50b60602c1084bf989c2503abac5b99fd6 Mon Sep 17 00:00:00 2001 From: Xin Li Date: Thu, 26 Jun 2025 10:35:21 -0700 Subject: [PATCH] KVM: x86: Advertise support for LKGS MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Advertise support for LKGS (load into IA32_KERNEL_GS_BASE) to userspace if the instruction is supported by the underlying CPU. LKGS is introduced with FRED to completely eliminate the need to swapgs explicilty. It behaves like the MOV to GS instruction except that it loads the base address into the IA32_KERNEL_GS_BASE MSR instead of the GS segment’s descriptor cache, which is exactly what Linux kernel does to load a user level GS base. Thus there is no need to SWAPGS away from the kernel GS base. LKGS is an independent CPU feature that works correctly in a KVM guest without requiring explicit enablement. Signed-off-by: Xin Li (Intel) Link: https://lore.kernel.org/r/20250626173521.2301088-1-xin@zytor.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/cpuid.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index b2d006756e02..bf4a43bd0a47 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -979,6 +979,7 @@ void kvm_set_cpu_caps(void) F(FSRS), F(FSRC), F(WRMSRNS), + X86_64_F(LKGS), F(AMX_FP16), F(AVX_IFMA), F(LAM), -- 2.47.3