KVM: VMX: Drop unnecessary vmx_fb_clear_ctrl_available "cache"

Now that KVM snapshots the host's MSR_IA32_ARCH_CAPABILITIES, drop the
similar snapshot/cache of whether or not KVM is allowed to manipulate
MSR_IA32_MCU_OPT_CTRL.FB_CLEAR_DIS.  The motivation for the cache was
presumably to avoid the RDMSR, e.g. boot_cpu_has_bug() is quite cheap, and
modifying the vCPU's MSR_IA32_ARCH_CAPABILITIES is an infrequent option
and a relatively slow path.

Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20230607004311.1420507-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f0ec9ac..e6d1ce2 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -237,9 +237,6 @@ static const struct {
 #define L1D_CACHE_ORDER 4
 static void *vmx_l1d_flush_pages;
 
-/* Control for disabling CPU Fill buffer clear */
-static bool __read_mostly vmx_fb_clear_ctrl_available;
-
 static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
 {
        struct page *page;
@@ -366,14 +363,6 @@ static int vmentry_l1d_flush_get(char *s, const struct kernel_param *kp)
        return sysfs_emit(s, "%s\n", vmentry_l1d_param[l1tf_vmx_mitigation].option);
 }
 
-static void vmx_setup_fb_clear_ctrl(void)
-{
-       if ((host_arch_capabilities & ARCH_CAP_FB_CLEAR_CTRL) &&
-           !boot_cpu_has_bug(X86_BUG_MDS) &&
-           !boot_cpu_has_bug(X86_BUG_TAA))
-               vmx_fb_clear_ctrl_available = true;
-}
-
 static __always_inline void vmx_disable_fb_clear(struct vcpu_vmx *vmx)
 {
        u64 msr;
@@ -399,7 +388,9 @@ static __always_inline void vmx_enable_fb_clear(struct vcpu_vmx *vmx)
 
 static void vmx_update_fb_clear_dis(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 {
-       vmx->disable_fb_clear = vmx_fb_clear_ctrl_available;
+       vmx->disable_fb_clear = (host_arch_capabilities & ARCH_CAP_FB_CLEAR_CTRL) &&
+                               !boot_cpu_has_bug(X86_BUG_MDS) &&
+                               !boot_cpu_has_bug(X86_BUG_TAA);
 
        /*
         * If guest will not execute VERW, there is no need to set FB_CLEAR_DIS
@@ -8626,8 +8617,6 @@ static int __init vmx_init(void)
        if (r)
                goto err_l1d_flush;
 
-       vmx_setup_fb_clear_ctrl();
-
        for_each_possible_cpu(cpu) {
                INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));