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Message-ID: <CALzav=dZitAYUQhH_-46m-gSB-Q_N_E_GX5K0CaE3-CdafbXxA@mail.gmail.com>
Date:   Thu, 16 Feb 2017 13:23:38 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: remove code for lazy FPU handling

On Thu, Feb 16, 2017 at 1:33 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> The FPU is always active now when running KVM.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: David Matlack <dmatlack@...gle.com>

Glad to see this cleanup! Thanks for doing it.

> ---
>  arch/x86/include/asm/kvm_host.h |   3 --
>  arch/x86/kvm/cpuid.c            |   2 -
>  arch/x86/kvm/svm.c              |  43 ++-------------
>  arch/x86/kvm/vmx.c              | 112 ++++++----------------------------------
>  arch/x86/kvm/x86.c              |   7 +--
>  include/linux/kvm_host.h        |   1 -
>  6 files changed, 19 insertions(+), 149 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e4f13e714bcf..74ef58c8ff53 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -55,7 +55,6 @@
>  #define KVM_REQ_TRIPLE_FAULT      10
>  #define KVM_REQ_MMU_SYNC          11
>  #define KVM_REQ_CLOCK_UPDATE      12
> -#define KVM_REQ_DEACTIVATE_FPU    13
>  #define KVM_REQ_EVENT             14
>  #define KVM_REQ_APF_HALT          15
>  #define KVM_REQ_STEAL_UPDATE      16
> @@ -936,8 +935,6 @@ struct kvm_x86_ops {
>         unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
>         void (*set_rflags)(struct kvm_vcpu *vcpu, unsigned long rflags);
>         u32 (*get_pkru)(struct kvm_vcpu *vcpu);
> -       void (*fpu_activate)(struct kvm_vcpu *vcpu);
> -       void (*fpu_deactivate)(struct kvm_vcpu *vcpu);
>
>         void (*tlb_flush)(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c0e2036217ad..1d155cc56629 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -123,8 +123,6 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>         if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
>                 best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
>
> -       kvm_x86_ops->fpu_activate(vcpu);
> -
>         /*
>          * The existing code assumes virtual address is 48-bit in the canonical
>          * address checks; exit if it is ever changed.
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 4e5905a1ce70..d1efe2c62b3f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1157,7 +1157,6 @@ static void init_vmcb(struct vcpu_svm *svm)
>         struct vmcb_control_area *control = &svm->vmcb->control;
>         struct vmcb_save_area *save = &svm->vmcb->save;
>
> -       svm->vcpu.fpu_active = 1;
>         svm->vcpu.arch.hflags = 0;
>
>         set_cr_intercept(svm, INTERCEPT_CR0_READ);
> @@ -1899,15 +1898,12 @@ static void update_cr0_intercept(struct vcpu_svm *svm)
>         ulong gcr0 = svm->vcpu.arch.cr0;
>         u64 *hcr0 = &svm->vmcb->save.cr0;
>
> -       if (!svm->vcpu.fpu_active)
> -               *hcr0 |= SVM_CR0_SELECTIVE_MASK;
> -       else
> -               *hcr0 = (*hcr0 & ~SVM_CR0_SELECTIVE_MASK)
> -                       | (gcr0 & SVM_CR0_SELECTIVE_MASK);
> +       *hcr0 = (*hcr0 & ~SVM_CR0_SELECTIVE_MASK)
> +               | (gcr0 & SVM_CR0_SELECTIVE_MASK);
>
>         mark_dirty(svm->vmcb, VMCB_CR);
>
> -       if (gcr0 == *hcr0 && svm->vcpu.fpu_active) {
> +       if (gcr0 == *hcr0) {
>                 clr_cr_intercept(svm, INTERCEPT_CR0_READ);
>                 clr_cr_intercept(svm, INTERCEPT_CR0_WRITE);
>         } else {
> @@ -1938,8 +1934,6 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>         if (!npt_enabled)
>                 cr0 |= X86_CR0_PG | X86_CR0_WP;
>
> -       if (!vcpu->fpu_active)
> -               cr0 |= X86_CR0_TS;
>         /*
>          * re-enable caching here because the QEMU bios
>          * does not do it - this results in some delay at
> @@ -2158,22 +2152,6 @@ static int ac_interception(struct vcpu_svm *svm)
>         return 1;
>  }
>
> -static void svm_fpu_activate(struct kvm_vcpu *vcpu)
> -{
> -       struct vcpu_svm *svm = to_svm(vcpu);
> -
> -       clr_exception_intercept(svm, NM_VECTOR);
> -
> -       svm->vcpu.fpu_active = 1;
> -       update_cr0_intercept(svm);
> -}
> -
> -static int nm_interception(struct vcpu_svm *svm)
> -{
> -       svm_fpu_activate(&svm->vcpu);
> -       return 1;
> -}
> -
>  static bool is_erratum_383(void)
>  {
>         int err, i;
> @@ -2571,9 +2549,6 @@ static int nested_svm_exit_special(struct vcpu_svm *svm)
>                 if (!npt_enabled && svm->apf_reason == 0)
>                         return NESTED_EXIT_HOST;
>                 break;
> -       case SVM_EXIT_EXCP_BASE + NM_VECTOR:
> -               nm_interception(svm);
> -               break;
>         default:
>                 break;
>         }
> @@ -4018,7 +3993,6 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
>         [SVM_EXIT_EXCP_BASE + BP_VECTOR]        = bp_interception,
>         [SVM_EXIT_EXCP_BASE + UD_VECTOR]        = ud_interception,
>         [SVM_EXIT_EXCP_BASE + PF_VECTOR]        = pf_interception,
> -       [SVM_EXIT_EXCP_BASE + NM_VECTOR]        = nm_interception,
>         [SVM_EXIT_EXCP_BASE + MC_VECTOR]        = mc_interception,
>         [SVM_EXIT_EXCP_BASE + AC_VECTOR]        = ac_interception,
>         [SVM_EXIT_INTR]                         = intr_interception,
> @@ -5072,14 +5046,6 @@ static bool svm_has_wbinvd_exit(void)
>         return true;
>  }
>
> -static void svm_fpu_deactivate(struct kvm_vcpu *vcpu)
> -{
> -       struct vcpu_svm *svm = to_svm(vcpu);
> -
> -       set_exception_intercept(svm, NM_VECTOR);
> -       update_cr0_intercept(svm);
> -}
> -
>  #define PRE_EX(exit)  { .exit_code = (exit), \
>                         .stage = X86_ICPT_PRE_EXCEPT, }
>  #define POST_EX(exit) { .exit_code = (exit), \
> @@ -5340,9 +5306,6 @@ static inline void avic_post_state_restore(struct kvm_vcpu *vcpu)
>
>         .get_pkru = svm_get_pkru,
>
> -       .fpu_activate = svm_fpu_activate,
> -       .fpu_deactivate = svm_fpu_deactivate,
> -
>         .tlb_flush = svm_flush_tlb,
>
>         .run = svm_vcpu_run,
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 0e0b5d09597e..9856b73a21ad 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1856,7 +1856,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
>         u32 eb;
>
>         eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |
> -            (1u << NM_VECTOR) | (1u << DB_VECTOR) | (1u << AC_VECTOR);
> +            (1u << DB_VECTOR) | (1u << AC_VECTOR);
>         if ((vcpu->guest_debug &
>              (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==
>             (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP))
> @@ -1865,8 +1865,6 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
>                 eb = ~0;
>         if (enable_ept)
>                 eb &= ~(1u << PF_VECTOR); /* bypass_guest_pf = 0 */
> -       if (vcpu->fpu_active)
> -               eb &= ~(1u << NM_VECTOR);
>
>         /* When we are running a nested L2 guest and L1 specified for it a
>          * certain exception bitmap, we must trap the same exceptions and pass
> @@ -2340,25 +2338,6 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>         }
>  }
>
> -static void vmx_fpu_activate(struct kvm_vcpu *vcpu)
> -{
> -       ulong cr0;
> -
> -       if (vcpu->fpu_active)
> -               return;
> -       vcpu->fpu_active = 1;
> -       cr0 = vmcs_readl(GUEST_CR0);
> -       cr0 &= ~(X86_CR0_TS | X86_CR0_MP);
> -       cr0 |= kvm_read_cr0_bits(vcpu, X86_CR0_TS | X86_CR0_MP);
> -       vmcs_writel(GUEST_CR0, cr0);
> -       update_exception_bitmap(vcpu);
> -       vcpu->arch.cr0_guest_owned_bits = X86_CR0_TS;
> -       if (is_guest_mode(vcpu))
> -               vcpu->arch.cr0_guest_owned_bits &=
> -                       ~get_vmcs12(vcpu)->cr0_guest_host_mask;
> -       vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
> -}
> -
>  static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>
>  /*
> @@ -2377,33 +2356,6 @@ static inline unsigned long nested_read_cr4(struct vmcs12 *fields)
>                 (fields->cr4_read_shadow & fields->cr4_guest_host_mask);
>  }
>
> -static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
> -{
> -       /* Note that there is no vcpu->fpu_active = 0 here. The caller must
> -        * set this *before* calling this function.
> -        */
> -       vmx_decache_cr0_guest_bits(vcpu);
> -       vmcs_set_bits(GUEST_CR0, X86_CR0_TS | X86_CR0_MP);
> -       update_exception_bitmap(vcpu);
> -       vcpu->arch.cr0_guest_owned_bits = 0;
> -       vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
> -       if (is_guest_mode(vcpu)) {
> -               /*
> -                * L1's specified read shadow might not contain the TS bit,
> -                * so now that we turned on shadowing of this bit, we need to
> -                * set this bit of the shadow. Like in nested_vmx_run we need
> -                * nested_read_cr0(vmcs12), but vmcs12->guest_cr0 is not yet
> -                * up-to-date here because we just decached cr0.TS (and we'll
> -                * only update vmcs12->guest_cr0 on nested exit).
> -                */
> -               struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> -               vmcs12->guest_cr0 = (vmcs12->guest_cr0 & ~X86_CR0_TS) |
> -                       (vcpu->arch.cr0 & X86_CR0_TS);
> -               vmcs_writel(CR0_READ_SHADOW, nested_read_cr0(vmcs12));
> -       } else
> -               vmcs_writel(CR0_READ_SHADOW, vcpu->arch.cr0);
> -}
> -
>  static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>  {
>         unsigned long rflags, save_rflags;
> @@ -4232,9 +4184,6 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>         if (enable_ept)
>                 ept_update_paging_mode_cr0(&hw_cr0, cr0, vcpu);
>
> -       if (!vcpu->fpu_active)
> -               hw_cr0 |= X86_CR0_TS | X86_CR0_MP;
> -
>         vmcs_writel(CR0_READ_SHADOW, cr0);
>         vmcs_writel(GUEST_CR0, hw_cr0);
>         vcpu->arch.cr0 = cr0;
> @@ -5321,7 +5270,9 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
>         /* 22.2.1, 20.8.1 */
>         vm_entry_controls_init(vmx, vmcs_config.vmentry_ctrl);
>
> -       vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL);
> +       vmx->vcpu.arch.cr0_guest_owned_bits = X86_CR0_TS;
> +       vmcs_writel(CR0_GUEST_HOST_MASK, ~X86_CR0_TS);
> +
>         set_cr4_guest_host_mask(vmx);
>
>         if (vmx_xsaves_supported())
> @@ -5425,7 +5376,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>         vmx_set_cr0(vcpu, cr0); /* enter rmode */
>         vmx_set_cr4(vcpu, 0);
>         vmx_set_efer(vcpu, 0);
> -       vmx_fpu_activate(vcpu);
> +
>         update_exception_bitmap(vcpu);
>
>         vpid_sync_context(vmx->vpid);
> @@ -5698,11 +5649,6 @@ static int handle_exception(struct kvm_vcpu *vcpu)
>         if (is_nmi(intr_info))
>                 return 1;  /* already handled by vmx_vcpu_run() */
>
> -       if (is_no_device(intr_info)) {
> -               vmx_fpu_activate(vcpu);
> -               return 1;
> -       }
> -
>         if (is_invalid_opcode(intr_info)) {
>                 if (is_guest_mode(vcpu)) {
>                         kvm_queue_exception(vcpu, UD_VECTOR);
> @@ -5892,22 +5838,6 @@ static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
>                 return kvm_set_cr4(vcpu, val);
>  }
>
> -/* called to set cr0 as appropriate for clts instruction exit. */
> -static void handle_clts(struct kvm_vcpu *vcpu)
> -{
> -       if (is_guest_mode(vcpu)) {
> -               /*
> -                * We get here when L2 did CLTS, and L1 didn't shadow CR0.TS
> -                * but we did (!fpu_active). We need to keep GUEST_CR0.TS on,
> -                * just pretend it's off (also in arch.cr0 for fpu_activate).
> -                */
> -               vmcs_writel(CR0_READ_SHADOW,
> -                       vmcs_readl(CR0_READ_SHADOW) & ~X86_CR0_TS);
> -               vcpu->arch.cr0 &= ~X86_CR0_TS;
> -       } else
> -               vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
> -}
> -
>  static int handle_cr(struct kvm_vcpu *vcpu)
>  {
>         unsigned long exit_qualification, val;
> @@ -5953,9 +5883,9 @@ static int handle_cr(struct kvm_vcpu *vcpu)
>                 }
>                 break;
>         case 2: /* clts */
> -               handle_clts(vcpu);
> +               WARN_ONCE(1, "Guest should always own CR0.TS");
> +               vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
>                 trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
> -               vmx_fpu_activate(vcpu);
>                 return kvm_skip_emulated_instruction(vcpu);
>         case 1: /*mov from cr*/
>                 switch (cr) {
> @@ -10349,8 +10279,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>         }
>
>         /*
> -        * This sets GUEST_CR0 to vmcs12->guest_cr0, with possibly a modified
> -        * TS bit (for lazy fpu) and bits which we consider mandatory enabled.
> +        * This sets GUEST_CR0 to vmcs12->guest_cr0, possibly modifying those
> +        * bits which we consider mandatory enabled.
>          * The CR0_READ_SHADOW is what L2 should have expected to read given
>          * the specifications by L1; It's not enough to take
>          * vmcs12->cr0_read_shadow because on our cr0_guest_host_mask we we
> @@ -10963,24 +10893,15 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>         vmx_set_rflags(vcpu, X86_EFLAGS_FIXED);
>         /*
>          * Note that calling vmx_set_cr0 is important, even if cr0 hasn't
> -        * actually changed, because it depends on the current state of
> -        * fpu_active (which may have changed).
> -        * Note that vmx_set_cr0 refers to efer set above.
> +        * actually changed, because vmx_set_cr0 refers to efer set above.
> +        *
> +        * CR0_GUEST_HOST_MASK is already set in the original vmcs01
> +        * (KVM doesn't change it);
>          */
> +       vcpu->arch.cr0_guest_owned_bits = X86_CR0_TS;
>         vmx_set_cr0(vcpu, vmcs12->host_cr0);
> -       /*
> -        * If we did fpu_activate()/fpu_deactivate() during L2's run, we need
> -        * to apply the same changes to L1's vmcs. We just set cr0 correctly,
> -        * but we also need to update cr0_guest_host_mask and exception_bitmap.
> -        */
> -       update_exception_bitmap(vcpu);
> -       vcpu->arch.cr0_guest_owned_bits = (vcpu->fpu_active ? X86_CR0_TS : 0);
> -       vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
>
> -       /*
> -        * Note that CR4_GUEST_HOST_MASK is already set in the original vmcs01
> -        * (KVM doesn't change it)- no reason to call set_cr4_guest_host_mask();
> -        */
> +       /* Same as above - no reason to call set_cr4_guest_host_mask().  */
>         vcpu->arch.cr4_guest_owned_bits = ~vmcs_readl(CR4_GUEST_HOST_MASK);
>         kvm_set_cr4(vcpu, vmcs12->host_cr4);
>
> @@ -11609,9 +11530,6 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
>
>         .get_pkru = vmx_get_pkru,
>
> -       .fpu_activate = vmx_fpu_activate,
> -       .fpu_deactivate = vmx_fpu_deactivate,
> -
>         .tlb_flush = vmx_flush_tlb,
>
>         .run = vmx_vcpu_run,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8d3047c8cce7..c48404017e4f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6751,10 +6751,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>                         r = 0;
>                         goto out;
>                 }
> -               if (kvm_check_request(KVM_REQ_DEACTIVATE_FPU, vcpu)) {
> -                       vcpu->fpu_active = 0;
> -                       kvm_x86_ops->fpu_deactivate(vcpu);
> -               }
>                 if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
>                         /* Page is swapped out. Do synthetic halt */
>                         vcpu->arch.apf.halted = true;
> @@ -6856,8 +6852,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>         preempt_disable();
>
>         kvm_x86_ops->prepare_guest_switch(vcpu);
> -       if (vcpu->fpu_active)
> -               kvm_load_guest_fpu(vcpu);
> +       kvm_load_guest_fpu(vcpu);
>
>         /*
>          * Disable IRQs before setting IN_GUEST_MODE.  Posted interrupt
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2db458ee94b0..8d69d5150748 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -221,7 +221,6 @@ struct kvm_vcpu {
>         struct mutex mutex;
>         struct kvm_run *run;
>
> -       int fpu_active;
>         int guest_fpu_loaded, guest_xcr0_loaded;
>         struct swait_queue_head wq;
>         struct pid *pid;
> --
> 1.8.3.1
>

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