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x86/KVM/VMX: Add L1D flush logic 

Add the logic for flushing L1D on VMENTER. The flush depends on the static
key being enabled and the new l1tf_flush_l1d flag being set.

The flags is set:
 - Always, if the flush module parameter is 'always'

 - Conditionally at:
   - Entry to vcpu_run(), i.e. after executing user space

   - From the sched_in notifier, i.e. when switching to a vCPU thread.

   - From vmexit handlers which are considered unsafe, i.e. where
     sensitive data can be brought into L1D:

     - The emulator, which could be a good target for other speculative
       execution-based threats,

     - The MMU, which can bring host page tables in the L1 cache.
     
     - External interrupts

     - Nested operations that require the MMU (see above). That is
       vmptrld, vmptrst, vmclear,vmwrite,vmread.

     - When handling invept,invvpid

[ tglx: Split out from combo patch and reduced to a single flag ]

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Paolo Bonzini 2018-07-02 13:07:14 +02:00 committed by Thomas Gleixner
parent 3fa045be4c
commit c595ceee45
4 changed files with 34 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/include/asm/kvm_host.h
View File

@ -713,6 +713,9 @@ struct kvm_vcpu_arch {
/* be preempted when it's in kernel-mode(cpl=0) */
bool preempted_in_kernel;
/* Flush the L1 Data cache for L1TF mitigation on VMENTER */
bool l1tf_flush_l1d;
};
struct kvm_lpage_info {
@ -881,6 +884,7 @@ struct kvm_vcpu_stat {
u64 signal_exits;
u64 irq_window_exits;
u64 nmi_window_exits;
u64 l1d_flush;
u64 halt_exits;
u64 halt_successful_poll;
u64 halt_attempted_poll;

1
arch/x86/kvm/mmu.c
View File

@ -3840,6 +3840,7 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
{
int r = 1;
vcpu->arch.l1tf_flush_l1d = true;
switch (vcpu->arch.apf.host_apf_reason) {
default:
trace_kvm_page_fault(fault_address, error_code);

22
arch/x86/kvm/vmx.c
View File

@ -9576,9 +9576,20 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
#define L1D_CACHE_ORDER 4
static void *vmx_l1d_flush_pages;
static void __maybe_unused vmx_l1d_flush(void)
static void vmx_l1d_flush(struct kvm_vcpu *vcpu)
{
int size = PAGE_SIZE << L1D_CACHE_ORDER;
bool always;
/*
* If the mitigation mode is 'flush always', keep the flush bit
* set, otherwise clear it. It gets set again either from
* vcpu_run() or from one of the unsafe VMEXIT handlers.
*/
always = vmentry_l1d_flush == VMENTER_L1D_FLUSH_ALWAYS;
vcpu->arch.l1tf_flush_l1d = always;
vcpu->stat.l1d_flush++;
if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
@ -9847,6 +9858,7 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
[ss]"i"(__KERNEL_DS),
[cs]"i"(__KERNEL_CS)
);
vcpu->arch.l1tf_flush_l1d = true;
}
}
STACK_FRAME_NON_STANDARD(vmx_handle_external_intr);
@ -10104,6 +10116,11 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
evmcs_rsp = static_branch_unlikely(&enable_evmcs) ?
(unsigned long)&current_evmcs->host_rsp : 0;
if (static_branch_unlikely(&vmx_l1d_should_flush)) {
if (vcpu->arch.l1tf_flush_l1d)
vmx_l1d_flush(vcpu);
}
asm(
/* Store host registers */
"push %%" _ASM_DX "; push %%" _ASM_BP ";"
@ -11917,6 +11934,9 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
return ret;
}
/* Hide L1D cache contents from the nested guest. */
vmx->vcpu.arch.l1tf_flush_l1d = true;
/*
* If we're entering a halted L2 vcpu and the L2 vcpu won't be woken
* by event injection, halt vcpu.

8
arch/x86/kvm/x86.c
View File

@ -195,6 +195,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
{ "irq_injections", VCPU_STAT(irq_injections) },
{ "nmi_injections", VCPU_STAT(nmi_injections) },
{ "req_event", VCPU_STAT(req_event) },
{ "l1d_flush", VCPU_STAT(l1d_flush) },
{ "mmu_shadow_zapped", VM_STAT(mmu_shadow_zapped) },
{ "mmu_pte_write", VM_STAT(mmu_pte_write) },
{ "mmu_pte_updated", VM_STAT(mmu_pte_updated) },
@ -4874,6 +4875,9 @@ static int emulator_write_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *v
int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val,
unsigned int bytes, struct x86_exception *exception)
{
/* kvm_write_guest_virt_system can pull in tons of pages. */
vcpu->arch.l1tf_flush_l1d = true;
return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
PFERR_WRITE_MASK, exception);
}
@ -6050,6 +6054,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
bool writeback = true;
bool write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
vcpu->arch.l1tf_flush_l1d = true;
/*
* Clear write_fault_to_shadow_pgtable here to ensure it is
* never reused.
@ -7579,6 +7585,7 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
struct kvm *kvm = vcpu->kvm;
vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
vcpu->arch.l1tf_flush_l1d = true;
for (;;) {
if (kvm_vcpu_running(vcpu)) {
@ -8698,6 +8705,7 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
{
vcpu->arch.l1tf_flush_l1d = true;
kvm_x86_ops->sched_in(vcpu, cpu);
}