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Message-ID: <CAAhV-H6VpRzxAvVVifoXXHGK=46R4uO+Jp2aSbzsW-Gr0QPfHQ@mail.gmail.com>
Date: Sun, 23 Jun 2024 18:11:38 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org, 
	loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] LoongArch: KVM: Add HW Binary Translation
 extension support

Hi, Bibo,

On Mon, May 27, 2024 at 3:46 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> Loongson Binary Translation (LBT) is used to accelerate binary translation,
> which contains 4 scratch registers (scr0 to scr3), x86/ARM eflags (eflags)
> and x87 fpu stack pointer (ftop).
>
> Like FPU extension, here late enabling method is used for LBT. LBT context
> is saved/restored on vcpu context switch path.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/loongarch/include/asm/kvm_host.h |  8 ++++
>  arch/loongarch/include/asm/kvm_vcpu.h | 10 +++++
>  arch/loongarch/kvm/exit.c             |  9 ++++
>  arch/loongarch/kvm/vcpu.c             | 59 ++++++++++++++++++++++++++-
>  4 files changed, 85 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 2eb2f7572023..88023ab59486 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -133,6 +133,7 @@ enum emulation_result {
>  #define KVM_LARCH_LASX         (0x1 << 2)
>  #define KVM_LARCH_SWCSR_LATEST (0x1 << 3)
>  #define KVM_LARCH_HWCSR_USABLE (0x1 << 4)
> +#define KVM_LARCH_LBT          (0x1 << 5)
>
>  struct kvm_vcpu_arch {
>         /*
> @@ -166,6 +167,7 @@ struct kvm_vcpu_arch {
>
>         /* FPU state */
>         struct loongarch_fpu fpu FPU_ALIGN;
> +       struct loongarch_lbt lbt;
>
>         /* CSR state */
>         struct loongarch_csrs *csr;
> @@ -235,6 +237,12 @@ static inline bool kvm_guest_has_lasx(struct kvm_vcpu_arch *arch)
>         return arch->cpucfg[2] & CPUCFG2_LASX;
>  }
>
> +static inline bool kvm_guest_has_lbt(struct kvm_vcpu_arch *arch)
> +{
> +       return arch->cpucfg[2] & (CPUCFG2_X86BT | CPUCFG2_ARMBT
> +                                       | CPUCFG2_MIPSBT);
> +}
> +
>  /* Debug: dump vcpu state */
>  int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/loongarch/include/asm/kvm_vcpu.h b/arch/loongarch/include/asm/kvm_vcpu.h
> index d7e51300a89f..ec46009be29b 100644
> --- a/arch/loongarch/include/asm/kvm_vcpu.h
> +++ b/arch/loongarch/include/asm/kvm_vcpu.h
> @@ -75,6 +75,16 @@ static inline void kvm_save_lasx(struct loongarch_fpu *fpu) { }
>  static inline void kvm_restore_lasx(struct loongarch_fpu *fpu) { }
>  #endif
>
> +#ifdef CONFIG_CPU_HAS_LBT
> +int kvm_own_lbt(struct kvm_vcpu *vcpu);
> +#else
> +static inline int kvm_own_lbt(struct kvm_vcpu *vcpu) { return -EINVAL; }
> +static inline void kvm_lose_lbt(struct kvm_vcpu *vcpu) { }
> +static inline void kvm_enable_lbt_fpu(struct kvm_vcpu *vcpu,
> +                                       unsigned long fcsr) { }
> +static inline void kvm_check_fcsr(struct kvm_vcpu *vcpu) { }
> +#endif
It is better to keep symmetry here. That means also declare
kvm_lose_lbt for CONFIG_CPU_HAS_LBT, and move the last two functions
to .c because they are static.

> +
>  void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long hz);
>  void kvm_reset_timer(struct kvm_vcpu *vcpu);
>  void kvm_save_timer(struct kvm_vcpu *vcpu);
> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
> index e2abd97fb13f..e1bd81d27fd8 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -835,6 +835,14 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
>         return ret;
>  }
>
> +static int kvm_handle_lbt_disabled(struct kvm_vcpu *vcpu)
> +{
> +       if (kvm_own_lbt(vcpu))
> +               kvm_queue_exception(vcpu, EXCCODE_INE, 0);
> +
> +       return RESUME_GUEST;
> +}
> +
>  /*
>   * LoongArch KVM callback handling for unimplemented guest exiting
>   */
> @@ -867,6 +875,7 @@ static exit_handle_fn kvm_fault_tables[EXCCODE_INT_START] = {
>         [EXCCODE_LASXDIS]               = kvm_handle_lasx_disabled,
>         [EXCCODE_GSPR]                  = kvm_handle_gspr,
>         [EXCCODE_HVC]                   = kvm_handle_hypercall,
> +       [EXCCODE_BTDIS]                 = kvm_handle_lbt_disabled,
>  };
>
>  int kvm_handle_fault(struct kvm_vcpu *vcpu, int fault)
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 382796f1d3e6..8f80d1a2dcbb 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -6,6 +6,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/entry-kvm.h>
>  #include <asm/fpu.h>
> +#include <asm/lbt.h>
>  #include <asm/loongarch.h>
>  #include <asm/setup.h>
>  #include <asm/time.h>
> @@ -952,12 +953,64 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
>         return 0;
>  }
>
> +#ifdef CONFIG_CPU_HAS_LBT
> +int kvm_own_lbt(struct kvm_vcpu *vcpu)
> +{
> +       if (!kvm_guest_has_lbt(&vcpu->arch))
> +               return -EINVAL;
> +
> +       preempt_disable();
> +       set_csr_euen(CSR_EUEN_LBTEN);
> +
> +       _restore_lbt(&vcpu->arch.lbt);
> +       vcpu->arch.aux_inuse |= KVM_LARCH_LBT;
> +       preempt_enable();
> +       return 0;
> +}
> +
> +static void kvm_lose_lbt(struct kvm_vcpu *vcpu)
> +{
> +       preempt_disable();
> +       if (vcpu->arch.aux_inuse & KVM_LARCH_LBT) {
> +               _save_lbt(&vcpu->arch.lbt);
> +               clear_csr_euen(CSR_EUEN_LBTEN);
> +               vcpu->arch.aux_inuse &= ~KVM_LARCH_LBT;
> +       }
> +       preempt_enable();
> +}
> +
> +static void kvm_enable_lbt_fpu(struct kvm_vcpu *vcpu, unsigned long fcsr)
It is better to rename it to kvm_own_lbt_tm().

> +{
> +       /*
> +        * if TM is enabled, top register save/restore will
> +        * cause lbt exception, here enable lbt in advance
> +        */
> +       if (fcsr & FPU_CSR_TM)
> +               kvm_own_lbt(vcpu);
> +}
> +
> +static void kvm_check_fcsr(struct kvm_vcpu *vcpu)
> +{
> +       unsigned long fcsr;
> +
> +       if (vcpu->arch.aux_inuse & KVM_LARCH_FPU)
> +               if (!(vcpu->arch.aux_inuse & KVM_LARCH_LBT)) {
The condition can be simplified " if (vcpu->arch.aux_inuse &
(KVM_LARCH_FPU|KVM_LARCH_LBT) == KVM_LARCH_FPU)"

> +                       fcsr = read_fcsr(LOONGARCH_FCSR0);
> +                       kvm_enable_lbt_fpu(vcpu, fcsr);
> +               }
> +}
> +#endif
> +
>  /* Enable FPU and restore context */
>  void kvm_own_fpu(struct kvm_vcpu *vcpu)
>  {
>         preempt_disable();
>
> -       /* Enable FPU */
> +       /*
> +        * Enable FPU for guest
> +        * We set FR and FRE according to guest context
> +        */
> +       kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
>         set_csr_euen(CSR_EUEN_FPEN);
>
>         kvm_restore_fpu(&vcpu->arch.fpu);
> @@ -977,6 +1030,7 @@ int kvm_own_lsx(struct kvm_vcpu *vcpu)
>         preempt_disable();
>
>         /* Enable LSX for guest */
> +       kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
>         set_csr_euen(CSR_EUEN_LSXEN | CSR_EUEN_FPEN);
>         switch (vcpu->arch.aux_inuse & KVM_LARCH_FPU) {
>         case KVM_LARCH_FPU:
> @@ -1011,6 +1065,7 @@ int kvm_own_lasx(struct kvm_vcpu *vcpu)
>
>         preempt_disable();
>
> +       kvm_enable_lbt_fpu(vcpu, vcpu->arch.fpu.fcsr);
>         set_csr_euen(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
>         switch (vcpu->arch.aux_inuse & (KVM_LARCH_FPU | KVM_LARCH_LSX)) {
>         case KVM_LARCH_LSX:
> @@ -1042,6 +1097,7 @@ void kvm_lose_fpu(struct kvm_vcpu *vcpu)
>  {
>         preempt_disable();
>
> +       kvm_check_fcsr(vcpu);
>         if (vcpu->arch.aux_inuse & KVM_LARCH_LASX) {
>                 kvm_save_lasx(&vcpu->arch.fpu);
>                 vcpu->arch.aux_inuse &= ~(KVM_LARCH_LSX | KVM_LARCH_FPU | KVM_LARCH_LASX);
> @@ -1064,6 +1120,7 @@ void kvm_lose_fpu(struct kvm_vcpu *vcpu)
>                 /* Disable FPU */
>                 clear_csr_euen(CSR_EUEN_FPEN);
>         }
> +       kvm_lose_lbt(vcpu);
>
>         preempt_enable();
>  }
> --
> 2.39.3
>

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