Kernel/linux-next
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git synced 2025-01-08 15:04:45 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

kvm/x86: rework guest entry logic

Browse Source 
For consistency and clarity, migrate x86 over to the generic helpers for
guest timing and lockdep/RCU/tracing management, and remove the
x86-specific helpers.

Prior to this patch, the guest timing was entered in
kvm_guest_enter_irqoff() (called by svm_vcpu_enter_exit() and
svm_vcpu_enter_exit()), and was exited by the call to
vtime_account_guest_exit() within vcpu_enter_guest().

To minimize duplication and to more clearly balance entry and exit, both
entry and exit of guest timing are placed in vcpu_enter_guest(), using
the new guest_timing_{enter,exit}_irqoff() helpers. When context
tracking is used a small amount of additional time will be accounted
towards guests; tick-based accounting is unnaffected as IRQs are
disabled at this point and not enabled until after the return from the
guest.

This also corrects (benign) mis-balanced context tracking accounting
introduced in commits:

  ae95f566b3 ("KVM: X86: TSCDEADLINE MSR emulation fastpath")
  26efe2fd92 ("KVM: VMX: Handle preemption timer fastpath")

Where KVM can enter a guest multiple times, calling vtime_guest_enter()
without a corresponding call to vtime_account_guest_exit(), and with
vtime_account_system() called when vtime_account_guest() should be used.
As account_system_time() checks PF_VCPU and calls account_guest_time(),
this doesn't result in any functional problem, but is unnecessarily
confusing.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <20220201132926.3301912-4-mark.rutland@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Mark Rutland 2022-02-01 13:29:24 +00:00 committed by Paolo Bonzini
parent 72e3244512
commit b2d2af7e5d
4 changed files with 7 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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

@ -3630,7 +3630,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
struct vcpu_svm *svm = to_svm(vcpu);
unsigned long vmcb_pa = svm->current_vmcb->pa;
kvm_guest_enter_irqoff();
guest_state_enter_irqoff();
if (sev_es_guest(vcpu->kvm)) {
__svm_sev_es_vcpu_run(vmcb_pa);
@ -3650,7 +3650,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
vmload(__sme_page_pa(sd->save_area));
}
kvm_guest_exit_irqoff();
guest_state_exit_irqoff();
}
static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)

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

@ -6767,7 +6767,7 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
struct vcpu_vmx *vmx)
{
kvm_guest_enter_irqoff();
guest_state_enter_irqoff();
/* L1D Flush includes CPU buffer clear to mitigate MDS */
if (static_branch_unlikely(&vmx_l1d_should_flush))
@ -6783,7 +6783,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
vcpu->arch.cr2 = native_read_cr2();
kvm_guest_exit_irqoff();
guest_state_exit_irqoff();
}
static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)

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

@ -10088,6 +10088,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
set_debugreg(0, 7);
}
guest_timing_enter_irqoff();
for (;;) {
/*
* Assert that vCPU vs. VM APICv state is consistent. An APICv
@ -10172,7 +10174,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
* of accounting via context tracking, but the loss of accuracy is
* acceptable for all known use cases.
*/
vtime_account_guest_exit();
guest_timing_exit_irqoff();
if (lapic_in_kernel(vcpu)) {
s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;

45
arch/x86/kvm/x86.h
View File

@ -10,51 +10,6 @@
void kvm_spurious_fault(void);
static __always_inline void kvm_guest_enter_irqoff(void)
{
/*
* VMENTER enables interrupts (host state), but the kernel state is
* interrupts disabled when this is invoked. Also tell RCU about
* it. This is the same logic as for exit_to_user_mode().
*
* This ensures that e.g. latency analysis on the host observes
* guest mode as interrupt enabled.
*
* guest_enter_irqoff() informs context tracking about the
* transition to guest mode and if enabled adjusts RCU state
* accordingly.
*/
instrumentation_begin();
trace_hardirqs_on_prepare();
lockdep_hardirqs_on_prepare(CALLER_ADDR0);
instrumentation_end();
guest_enter_irqoff();
lockdep_hardirqs_on(CALLER_ADDR0);
}
static __always_inline void kvm_guest_exit_irqoff(void)
{
/*
* VMEXIT disables interrupts (host state), but tracing and lockdep
* have them in state 'on' as recorded before entering guest mode.
* Same as enter_from_user_mode().
*
* context_tracking_guest_exit() restores host context and reinstates
* RCU if enabled and required.
*
* This needs to be done immediately after VM-Exit, before any code
* that might contain tracepoints or call out to the greater world,
* e.g. before x86_spec_ctrl_restore_host().
*/
lockdep_hardirqs_off(CALLER_ADDR0);
context_tracking_guest_exit();
instrumentation_begin();
trace_hardirqs_off_finish();
instrumentation_end();
}
#define KVM_NESTED_VMENTER_CONSISTENCY_CHECK(consistency_check) \
({ \
bool failed = (consistency_check); \