[PATCH 2/2] KVM: VMX: Drop unnecessary vmx_fb_clear_ctrl_available "cache"

From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Chao Gao <chao.gao@intel.com>, Xiaoyao Li <xiaoyao.li@intel.com>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: [PATCH 2/2] KVM: VMX: Drop unnecessary vmx_fb_clear_ctrl_available "cache"
Date: Tue,  6 Jun 2023 17:43:10 -0700	[thread overview]
Message-ID: <20230607004311.1420507-3-seanjc@google.com> (raw)
In-Reply-To: <20230607004311.1420507-1-seanjc@google.com>

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
ARCH_CAPABILITIES.FB_CLEAR_CTRL.  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>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 42d1148f933c..17003660138a 100644
--- 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 sprintf(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
@@ -8580,8 +8571,6 @@ 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));
 
-- 
2.41.0.162.gfafddb0af9-goog

