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SubjectRe: [RFC PATCH v2 36/69] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior
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On 03/07/21 00:04, isaku.yamahata@intel.com wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Add a flag, KVM_DEBUGREG_AUTO_SWITCHED_GUEST, to skip saving/restoring DRs
> irrespective of any other flags. TDX-SEAM unconditionally saves and
> restores guest DRs and reset to architectural INIT state on TD exit.
> So, KVM needs to save host DRs before TD enter without restoring guest DRs
> and restore host DRs after TD exit.
>
> Opportunistically convert the KVM_DEBUGREG_* definitions to use BIT().
>
> Reported-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Co-developed-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
> arch/x86/include/asm/kvm_host.h | 11 ++++++++---
> arch/x86/kvm/x86.c | 3 ++-
> 2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 96e6cd95d884..7822b531a5e2 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -488,9 +488,14 @@ struct kvm_pmu {
> struct kvm_pmu_ops;
>
> enum {
> - KVM_DEBUGREG_BP_ENABLED = 1,
> - KVM_DEBUGREG_WONT_EXIT = 2,
> - KVM_DEBUGREG_RELOAD = 4,
> + KVM_DEBUGREG_BP_ENABLED = BIT(0),
> + KVM_DEBUGREG_WONT_EXIT = BIT(1),
> + KVM_DEBUGREG_RELOAD = BIT(2),
> + /*
> + * Guest debug registers are saved/restored by hardware on exit from
> + * or enter guest. KVM needn't switch them.
> + */
> + KVM_DEBUGREG_AUTO_SWITCH_GUEST = BIT(3),

Maybe remove "_GUEST"? Apart from that,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

> };
>
> struct kvm_mtrr_range {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4b436cae1732..f1d5e0a53640 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9441,7 +9441,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> if (test_thread_flag(TIF_NEED_FPU_LOAD))
> switch_fpu_return();
>
> - if (unlikely(vcpu->arch.switch_db_regs)) {
> + if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH_GUEST)) {
> set_debugreg(0, 7);
> set_debugreg(vcpu->arch.eff_db[0], 0);
> set_debugreg(vcpu->arch.eff_db[1], 1);
> @@ -9473,6 +9473,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> */
> if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) {
> WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP);
> + WARN_ON(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH_GUEST);
> static_call(kvm_x86_sync_dirty_debug_regs)(vcpu);
> kvm_update_dr0123(vcpu);
> kvm_update_dr7(vcpu);
>

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