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

Sean Christopherson
2023-06-07T00:43:27Z

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