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KVM: x86: Add wrapper APIs to reset dirty/available register masks

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Add wrappers for setting regs_{avail,dirty} in anticipation of turning the
fields into proper bitmaps, at which point direct writes won't work so
well.

Deliberately leave the initialization in kvm_arch_vcpu_create() as-is,
because the regs_avail logic in particular is special in that it's the one
and only place where KVM marks eagerly synchronized registers as available.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260409224236.2021562-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2026-04-09 15:42:33 -07:00 committed by Paolo Bonzini
parent 3b628ef168
commit 0af556e6f9
5 changed files with 25 additions and 7 deletions
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18
arch/x86/kvm/kvm_cache_regs.h
View File

@ -105,6 +105,24 @@ static __always_inline bool kvm_register_test_and_mark_available(struct kvm_vcpu
return arch___test_and_set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
}
static __always_inline void kvm_clear_available_registers(struct kvm_vcpu *vcpu,
u32 clear_mask)
{
/*
* Note the bitwise-AND! In practice, a straight write would also work
* as KVM initializes the mask to all ones and never clears registers
* that are eagerly synchronized. Using a bitwise-AND adds a bit of
* sanity checking as incorrectly marking an eagerly sync'd register
* unavailable will generate a WARN due to an unexpected cache request.
*/
vcpu->arch.regs_avail &= ~clear_mask;
}
static __always_inline void kvm_reset_dirty_registers(struct kvm_vcpu *vcpu)
{
vcpu->arch.regs_dirty = 0;
}
/*
* The "raw" register helpers are only for cases where the full 64 bits of a
* register are read/written irrespective of current vCPU mode. In other words,

4
arch/x86/kvm/svm/svm.c
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@ -4508,7 +4508,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;
vcpu->arch.rip = svm->vmcb->save.rip;
}
vcpu->arch.regs_dirty = 0;
kvm_reset_dirty_registers(vcpu);
if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
@ -4554,7 +4554,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
vcpu->arch.apf.host_apf_flags =
kvm_read_and_reset_apf_flags();
vcpu->arch.regs_avail &= ~SVM_REGS_LAZY_LOAD_SET;
kvm_clear_available_registers(vcpu, SVM_REGS_LAZY_LOAD_SET);
if (!msr_write_intercepted(vcpu, MSR_AMD64_PERF_CNTR_GLOBAL_CTL))
rdmsrq(MSR_AMD64_PERF_CNTR_GLOBAL_CTL, vcpu_to_pmu(vcpu)->global_ctrl);

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

@ -310,13 +310,13 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
vmx_sync_vmcs_host_state(vmx, prev);
put_cpu();
vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
kvm_clear_available_registers(vcpu, VMX_REGS_LAZY_LOAD_SET);
/*
* All lazily updated registers will be reloaded from VMCS12 on both
* vmentry and vmexit.
*/
vcpu->arch.regs_dirty = 0;
kvm_reset_dirty_registers(vcpu);
}
static void nested_put_vmcs12_pages(struct kvm_vcpu *vcpu)

2
arch/x86/kvm/vmx/tdx.c
View File

@ -1098,7 +1098,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
tdx_load_host_xsave_state(vcpu);
vcpu->arch.regs_avail &= TDX_REGS_AVAIL_SET;
kvm_clear_available_registers(vcpu, ~(u32)TDX_REGS_AVAIL_SET);
if (unlikely(tdx->vp_enter_ret == EXIT_REASON_EPT_MISCONFIG))
return EXIT_FASTPATH_NONE;

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

@ -7472,7 +7472,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
flags);
vcpu->arch.cr2 = native_read_cr2();
vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
kvm_clear_available_registers(vcpu, VMX_REGS_LAZY_LOAD_SET);
vmx->idt_vectoring_info = 0;
@ -7538,7 +7538,7 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]);
if (kvm_register_is_dirty(vcpu, VCPU_REG_RIP))
vmcs_writel(GUEST_RIP, vcpu->arch.rip);
vcpu->arch.regs_dirty = 0;
kvm_reset_dirty_registers(vcpu);
if (run_flags & KVM_RUN_LOAD_GUEST_DR6)
set_debugreg(vcpu->arch.dr6, 6);