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x86/bugs: Use an x86 feature to track the MMIO Stale Data mitigation

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Convert the MMIO Stale Data mitigation tracking from a static branch into
an x86 feature flag so that it can be used via ALTERNATIVE_2 in KVM.

No functional change intended.

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Link: https://patch.msgid.link/20251113233746.1703361-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2025-11-13 15:37:41 -08:00
parent afb99ffbd5
commit f6106d41ec
5 changed files with 9 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/include/asm/cpufeatures.h
View File

@@ -499,6 +499,11 @@
#define X86_FEATURE_IBPB_EXIT_TO_USER (21*32+14) /* Use IBPB on exit-to-userspace, see VMSCAPE bug */
#define X86_FEATURE_ABMC (21*32+15) /* Assignable Bandwidth Monitoring Counters */
#define X86_FEATURE_MSR_IMM (21*32+16) /* MSR immediate form instructions */
#define X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO (21*32+17) /*
* Clear CPU buffers before VM-Enter if the vCPU
* can access host MMIO (ignored for all intents
* and purposes if CLEAR_CPU_BUF_VM is set).
*/
/*
* BUG word(s)

2
arch/x86/include/asm/nospec-branch.h
View File

@@ -585,8 +585,6 @@ DECLARE_STATIC_KEY_FALSE(cpu_buf_idle_clear);
DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear);
extern u16 x86_verw_sel;
#include <asm/segment.h>

11
arch/x86/kernel/cpu/bugs.c
View File

@@ -192,14 +192,6 @@ EXPORT_SYMBOL_GPL(cpu_buf_idle_clear);
*/
DEFINE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
/*
* Controls CPU Fill buffer clear before VMenter. This is a subset of
* X86_FEATURE_CLEAR_CPU_BUF_VM, and should only be enabled when KVM-only
* mitigation is required.
*/
DEFINE_STATIC_KEY_FALSE(cpu_buf_vm_clear);
EXPORT_SYMBOL_GPL(cpu_buf_vm_clear);
#undef pr_fmt
#define pr_fmt(fmt) "mitigations: " fmt
@@ -751,9 +743,8 @@ static void __init mmio_apply_mitigation(void)
if (verw_clear_cpu_buf_mitigation_selected) {
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF_VM);
static_branch_disable(&cpu_buf_vm_clear);
} else {
static_branch_enable(&cpu_buf_vm_clear);
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO);
}
/*

2
arch/x86/kvm/mmu/spte.c
View File

@@ -292,7 +292,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
mark_page_dirty_in_slot(vcpu->kvm, slot, gfn);
}
if (static_branch_unlikely(&cpu_buf_vm_clear) &&
if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO) &&
!kvm_vcpu_can_access_host_mmio(vcpu) &&
kvm_is_mmio_pfn(pfn, &is_host_mmio))
kvm_track_host_mmio_mapping(vcpu);

4
arch/x86/kvm/vmx/vmx.c
View File

@@ -903,7 +903,7 @@ unsigned int __vmx_vcpu_run_flags(struct vcpu_vmx *vmx)
if (!msr_write_intercepted(vmx, MSR_IA32_SPEC_CTRL))
flags |= VMX_RUN_SAVE_SPEC_CTRL;
if (static_branch_unlikely(&cpu_buf_vm_clear) &&
if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO) &&
kvm_vcpu_can_access_host_mmio(&vmx->vcpu))
flags |= VMX_RUN_CLEAR_CPU_BUFFERS_FOR_MMIO;
@@ -7325,7 +7325,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
*/
if (static_branch_unlikely(&vmx_l1d_should_flush))
vmx_l1d_flush(vcpu);
else if (static_branch_unlikely(&cpu_buf_vm_clear) &&
else if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO) &&
(flags & VMX_RUN_CLEAR_CPU_BUFFERS_FOR_MMIO))
x86_clear_cpu_buffers();