[PATCH v3 2/4] KVM: VMX: Bundle all L1 data cache flush mitigation code together

Sean Christopherson
2025-10-16T20:04:25Z

Move vmx_l1d_flush(), vmx_cleanup_l1d_flush(), and the vmentry_l1d_flush
param code up in vmx.c so that all of the L1 data cache flushing code is
bundled together. This will allow conditioning the mitigation code on
CONFIG_CPU_MITIGATIONS=y with minimal #ifdefs.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 176 ++++++++++++++++++++---------------------
1 file changed, 88 insertions(+), 88 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ce556d5dc39b..cd8ae1b2ae55 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -302,6 +302,16 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
return 0;
}

+static void vmx_cleanup_l1d_flush(void)
+{
+ if (vmx_l1d_flush_pages) {
+ free_pages((unsigned long)vmx_l1d_flush_pages, L1D_CACHE_ORDER);
+ vmx_l1d_flush_pages = NULL;
+ }
+ /* Restore state so sysfs ignores VMX */
+ l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
+}
+
static int vmentry_l1d_flush_parse(const char *s)
{
unsigned int i;
@@ -352,6 +362,84 @@ 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);
}

+/*
+ * Software based L1D cache flush which is used when microcode providing
+ * the cache control MSR is not loaded.
+ *
+ * The L1D cache is 32 KiB on Nehalem and later microarchitectures, but to
+ * flush it is required to read in 64 KiB because the replacement algorithm
+ * is not exactly LRU. This could be sized at runtime via topology
+ * information but as all relevant affected CPUs have 32KiB L1D cache size
+ * there is no point in doing so.
+ */
+static noinstr bool vmx_l1d_flush(struct kvm_vcpu *vcpu)
+{
+ int size = PAGE_SIZE << L1D_CACHE_ORDER;
+
+ /*
+ * This code is only executed when the flush mode is 'cond' or
+ * 'always'
+ */
+ if (static_branch_likely(&vmx_l1d_flush_cond)) {
+ bool flush_l1d;
+
+ /*
+ * Clear the per-vcpu flush bit, it gets set again if the vCPU
+ * is reloaded, i.e. if the vCPU is scheduled out or if KVM
+ * exits to userspace, or if KVM reaches one of the unsafe
+ * VMEXIT handlers, e.g. if KVM calls into the emulator.
+ */
+ flush_l1d = vcpu->arch.l1tf_flush_l1d;
+ vcpu->arch.l1tf_flush_l1d = false;
+
+ /*
+ * Clear the per-cpu flush bit, it gets set again from
+ * the interrupt handlers.
+ */
+ flush_l1d |= kvm_get_cpu_l1tf_flush_l1d();
+ kvm_clear_cpu_l1tf_flush_l1d();
+
+ if (!flush_l1d)
+ return false;
+ }
+
+ vcpu->stat.l1d_flush++;
+
+ if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
+ native_wrmsrq(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
+ return true;
+ }
+
+ asm volatile(
+ /* First ensure the pages are in the TLB */
+ "xorl %%eax, %%eax\n"
+ ".Lpopulate_tlb:\n\t"
+ "movzbl (%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
+ "addl $4096, %%eax\n\t"
+ "cmpl %%eax, %[size]\n\t"
+ "jne .Lpopulate_tlb\n\t"
+ "xorl %%eax, %%eax\n\t"
+ "cpuid\n\t"
+ /* Now fill the cache */
+ "xorl %%eax, %%eax\n"
+ ".Lfill_cache:\n"
+ "movzbl (%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
+ "addl $64, %%eax\n\t"
+ "cmpl %%eax, %[size]\n\t"
+ "jne .Lfill_cache\n\t"
+ "lfence\n"
+ :: [flush_pages] "r" (vmx_l1d_flush_pages),
+ [size] "r" (size)
+ : "eax", "ebx", "ecx", "edx");
+ return true;
+}
+
+static const struct kernel_param_ops vmentry_l1d_flush_ops = {
+ .set = vmentry_l1d_flush_set,
+ .get = vmentry_l1d_flush_get,
+};
+module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
+
static __always_inline void vmx_disable_fb_clear(struct vcpu_vmx *vmx)
{
u64 msr;
@@ -404,12 +492,6 @@ static void vmx_update_fb_clear_dis(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
vmx->disable_fb_clear = false;
}

-static const struct kernel_param_ops vmentry_l1d_flush_ops = {
- .set = vmentry_l1d_flush_set,
- .get = vmentry_l1d_flush_get,
-};
-module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
-
static u32 vmx_segment_access_rights(struct kvm_segment *var);

void vmx_vmexit(void);
@@ -6653,78 +6735,6 @@ int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return ret;
}

-/*
- * Software based L1D cache flush which is used when microcode providing
- * the cache control MSR is not loaded.
- *
- * The L1D cache is 32 KiB on Nehalem and later microarchitectures, but to
- * flush it is required to read in 64 KiB because the replacement algorithm
- * is not exactly LRU. This could be sized at runtime via topology
- * information but as all relevant affected CPUs have 32KiB L1D cache size
- * there is no point in doing so.
- */
-static noinstr bool vmx_l1d_flush(struct kvm_vcpu *vcpu)
-{
- int size = PAGE_SIZE << L1D_CACHE_ORDER;
-
- /*
- * This code is only executed when the flush mode is 'cond' or
- * 'always'
- */
- if (static_branch_likely(&vmx_l1d_flush_cond)) {
- bool flush_l1d;
-
- /*
- * Clear the per-vcpu flush bit, it gets set again if the vCPU
- * is reloaded, i.e. if the vCPU is scheduled out or if KVM
- * exits to userspace, or if KVM reaches one of the unsafe
- * VMEXIT handlers, e.g. if KVM calls into the emulator.
- */
- flush_l1d = vcpu->arch.l1tf_flush_l1d;
- vcpu->arch.l1tf_flush_l1d = false;
-
- /*
- * Clear the per-cpu flush bit, it gets set again from
- * the interrupt handlers.
- */
- flush_l1d |= kvm_get_cpu_l1tf_flush_l1d();
- kvm_clear_cpu_l1tf_flush_l1d();
-
- if (!flush_l1d)
- return false;
- }
-
- vcpu->stat.l1d_flush++;
-
- if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
- native_wrmsrq(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
- return true;
- }
-
- asm volatile(
- /* First ensure the pages are in the TLB */
- "xorl %%eax, %%eax\n"
- ".Lpopulate_tlb:\n\t"
- "movzbl (%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
- "addl $4096, %%eax\n\t"
- "cmpl %%eax, %[size]\n\t"
- "jne .Lpopulate_tlb\n\t"
- "xorl %%eax, %%eax\n\t"
- "cpuid\n\t"
- /* Now fill the cache */
- "xorl %%eax, %%eax\n"
- ".Lfill_cache:\n"
- "movzbl (%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
- "addl $64, %%eax\n\t"
- "cmpl %%eax, %[size]\n\t"
- "jne .Lfill_cache\n\t"
- "lfence\n"
- :: [flush_pages] "r" (vmx_l1d_flush_pages),
- [size] "r" (size)
- : "eax", "ebx", "ecx", "edx");
- return true;
-}
-
void vmx_update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
{
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
@@ -8673,16 +8683,6 @@ __init int vmx_hardware_setup(void)
return r;
}

-static void vmx_cleanup_l1d_flush(void)
-{
- if (vmx_l1d_flush_pages) {
- free_pages((unsigned long)vmx_l1d_flush_pages, L1D_CACHE_ORDER);
- vmx_l1d_flush_pages = NULL;
- }
- /* Restore state so sysfs ignores VMX */
- l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
-}
-
void vmx_exit(void)
{
allow_smaller_maxphyaddr = false;
--
2.51.0.858.gf9c4a03a3a-goog