Re: [PATCH] RISC-V: KVM: Improve ISA extension by using a bitmap

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On Mon, Jul 4, 2022 at 1:47 AM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
>
> On Tue, Jun 21, 2022 at 5:13 AM Atish Patra <atishp@xxxxxxxxxxxx> wrote:
> >
> > Currently, the every vcpu only stores the ISA extensions in a unsigned long
> > which is not scalable as number of extensions will continue to grow.
> > Using a bitmap allows the ISA extension to support any number of
> > extensions. The CONFIG one reg interface implementation is modified to
> > support the bitmap as well. But it is meant only for base extensions.
> > Thus, the first element of the bitmap array is sufficient for that
> > interface.
> >
> > In the future, all the new multi-letter extensions must use the
> > ISA_EXT one reg interface that allows enabling/disabling any extension
> > now.
> >
> > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> > ---
> >  arch/riscv/include/asm/kvm_host.h    |  3 +-
> >  arch/riscv/include/asm/kvm_vcpu_fp.h |  8 +--
> >  arch/riscv/kvm/vcpu.c                | 81 ++++++++++++++--------------
> >  arch/riscv/kvm/vcpu_fp.c             | 27 +++++-----
> >  4 files changed, 59 insertions(+), 60 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> > index 319c8aeb42af..c749cdacbd63 100644
> > --- a/arch/riscv/include/asm/kvm_host.h
> > +++ b/arch/riscv/include/asm/kvm_host.h
> > @@ -14,6 +14,7 @@
> >  #include <linux/kvm_types.h>
> >  #include <linux/spinlock.h>
> >  #include <asm/csr.h>
> > +#include <asm/hwcap.h>
> >  #include <asm/kvm_vcpu_fp.h>
> >  #include <asm/kvm_vcpu_timer.h>
> >
> > @@ -170,7 +171,7 @@ struct kvm_vcpu_arch {
> >         int last_exit_cpu;
> >
> >         /* ISA feature bits (similar to MISA) */
> > -       unsigned long isa;
> > +       DECLARE_BITMAP(isa, RISCV_ISA_EXT_MAX);
> >
> >         /* SSCRATCH, STVEC, and SCOUNTEREN of Host */
> >         unsigned long host_sscratch;
> > diff --git a/arch/riscv/include/asm/kvm_vcpu_fp.h b/arch/riscv/include/asm/kvm_vcpu_fp.h
> > index 4da9b8e0f050..e86bb67f2a8a 100644
> > --- a/arch/riscv/include/asm/kvm_vcpu_fp.h
> > +++ b/arch/riscv/include/asm/kvm_vcpu_fp.h
> > @@ -22,9 +22,9 @@ void __kvm_riscv_fp_d_restore(struct kvm_cpu_context *context);
> >
> >  void kvm_riscv_vcpu_fp_reset(struct kvm_vcpu *vcpu);
> >  void kvm_riscv_vcpu_guest_fp_save(struct kvm_cpu_context *cntx,
> > -                                 unsigned long isa);
> > +                                 unsigned long *isa);
>
> Better to use "const unsigned long *"
>
> >  void kvm_riscv_vcpu_guest_fp_restore(struct kvm_cpu_context *cntx,
> > -                                    unsigned long isa);
> > +                                    unsigned long *isa);
>
> Same as above.
>

Yes. Thanks.

> >  void kvm_riscv_vcpu_host_fp_save(struct kvm_cpu_context *cntx);
> >  void kvm_riscv_vcpu_host_fp_restore(struct kvm_cpu_context *cntx);
> >  #else
> > @@ -32,12 +32,12 @@ static inline void kvm_riscv_vcpu_fp_reset(struct kvm_vcpu *vcpu)
> >  {
> >  }
> >  static inline void kvm_riscv_vcpu_guest_fp_save(struct kvm_cpu_context *cntx,
> > -                                               unsigned long isa)
> > +                                               unsigned long *isa)
> >  {
> >  }
> >  static inline void kvm_riscv_vcpu_guest_fp_restore(
> >                                         struct kvm_cpu_context *cntx,
> > -                                       unsigned long isa)
> > +                                       unsigned long *isa)
> >  {
> >  }
> >  static inline void kvm_riscv_vcpu_host_fp_save(struct kvm_cpu_context *cntx)
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index 7f4ad5e4373a..cb2a65b5d563 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -46,8 +46,19 @@ const struct kvm_stats_header kvm_vcpu_stats_header = {
> >                                                 riscv_isa_extension_mask(i) | \
> >                                                 riscv_isa_extension_mask(m))
> >
> > -#define KVM_RISCV_ISA_ALLOWED (KVM_RISCV_ISA_DISABLE_ALLOWED | \
> > -                              KVM_RISCV_ISA_DISABLE_NOT_ALLOWED)
> > +#define KVM_RISCV_ISA_MASK GENMASK(25, 0)
> > +
> > +/* Mapping between KVM ISA Extension ID & Host ISA extension ID */
> > +static unsigned long kvm_isa_ext_arr[] = {
> > +       RISCV_ISA_EXT_a,
> > +       RISCV_ISA_EXT_c,
> > +       RISCV_ISA_EXT_d,
> > +       RISCV_ISA_EXT_f,
> > +       RISCV_ISA_EXT_h,
> > +       RISCV_ISA_EXT_i,
> > +       RISCV_ISA_EXT_m,
> > +       RISCV_ISA_EXT_SSCOFPMF,
>
> The RISCV_ISA_EXT_SSCOFPMF should be added only after we have
> SBI PMU support in KVM RISC-V. Please drop it.
>

Ahh. Sorry. I forgot to remove it while rebasing.

> > +};
> >
> >  static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)
> >  {
> > @@ -99,13 +110,20 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> >  {
> >         struct kvm_cpu_context *cntx;
> >         struct kvm_vcpu_csr *reset_csr = &vcpu->arch.guest_reset_csr;
> > +       unsigned long host_isa, i;
> >
> >         /* Mark this VCPU never ran */
> >         vcpu->arch.ran_atleast_once = false;
> >         vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
> > +       bitmap_zero(vcpu->arch.isa, RISCV_ISA_EXT_MAX);
> >
> >         /* Setup ISA features available to VCPU */
> > -       vcpu->arch.isa = riscv_isa_extension_base(NULL) & KVM_RISCV_ISA_ALLOWED;
> > +       for (i = 0; i < ARRAY_SIZE(kvm_isa_ext_arr); i++) {
> > +               host_isa = kvm_isa_ext_arr[i];
> > +               if (__riscv_isa_extension_available(NULL, host_isa) &&
> > +                  host_isa != RISCV_ISA_EXT_h)
> > +                       set_bit(host_isa, vcpu->arch.isa);
> > +       }
> >
> >         /* Setup VCPU hfence queue */
> >         spin_lock_init(&vcpu->arch.hfence_lock);
> > @@ -199,7 +217,7 @@ static int kvm_riscv_vcpu_get_reg_config(struct kvm_vcpu *vcpu,
> >
> >         switch (reg_num) {
> >         case KVM_REG_RISCV_CONFIG_REG(isa):
> > -               reg_val = vcpu->arch.isa;
> > +               reg_val = vcpu->arch.isa[0] & KVM_RISCV_ISA_MASK;
> >                 break;
> >         default:
> >                 return -EINVAL;
> > @@ -220,6 +238,7 @@ static int kvm_riscv_vcpu_set_reg_config(struct kvm_vcpu *vcpu,
> >                                             KVM_REG_SIZE_MASK |
> >                                             KVM_REG_RISCV_CONFIG);
> >         unsigned long reg_val;
> > +       unsigned long isa_mask;
> >
> >         if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> >                 return -EINVAL;
> > @@ -227,13 +246,19 @@ static int kvm_riscv_vcpu_set_reg_config(struct kvm_vcpu *vcpu,
> >         if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
> >                 return -EFAULT;
> >
> > +       /* This ONE REG interface is only defined for single letter extensions */
> > +       if (fls(reg_val) >= RISCV_ISA_EXT_BASE)
> > +               return -EINVAL;
> > +
> >         switch (reg_num) {
> >         case KVM_REG_RISCV_CONFIG_REG(isa):
> >                 if (!vcpu->arch.ran_atleast_once) {
> >                         /* Ignore the disable request for these extensions */
> > -                       vcpu->arch.isa = reg_val | KVM_RISCV_ISA_DISABLE_NOT_ALLOWED;
> > -                       vcpu->arch.isa &= riscv_isa_extension_base(NULL);
> > -                       vcpu->arch.isa &= KVM_RISCV_ISA_ALLOWED;
> > +                       isa_mask = (reg_val | KVM_RISCV_ISA_DISABLE_NOT_ALLOWED);
> > +                       isa_mask &= riscv_isa_extension_base(NULL);
> > +                       /* Do not modify anything beyond single letter extensions */
> > +                       isa_mask |= (~KVM_RISCV_ISA_MASK);
> > +                       bitmap_and(vcpu->arch.isa, vcpu->arch.isa, &isa_mask, RISCV_ISA_EXT_MAX);
>
> A little more readable version of above sequence can be:
>
>             /* Ignore the disable request for these extensions */
>             reg_val |= KVM_RISCV_ISA_DISABLE_NOT_ALLOWED;
>             reg_val &= riscv_isa_extension_base(NULL);
>             /* Do not modify anything beyond single letter extensions */
>             reg_val = (vcpu->arch.isa[0] & ~KVM_RISCV_ISA_MASK) |
>                   (reg_val & KVM_RISCV_ISA_MASK);
>             vcpu->arch.isa[0] = reg_val;
>             kvm_riscv_vcpu_fp_reset(vcpu);
>
>
> >                         kvm_riscv_vcpu_fp_reset(vcpu);
> >                 } else {
> >                         return -EOPNOTSUPP;
> > @@ -374,17 +399,6 @@ static int kvm_riscv_vcpu_set_reg_csr(struct kvm_vcpu *vcpu,
> >         return 0;
> >  }
> >
> > -/* Mapping between KVM ISA Extension ID & Host ISA extension ID */
> > -static unsigned long kvm_isa_ext_arr[] = {
> > -       RISCV_ISA_EXT_a,
> > -       RISCV_ISA_EXT_c,
> > -       RISCV_ISA_EXT_d,
> > -       RISCV_ISA_EXT_f,
> > -       RISCV_ISA_EXT_h,
> > -       RISCV_ISA_EXT_i,
> > -       RISCV_ISA_EXT_m,
> > -};
> > -
> >  static int kvm_riscv_vcpu_get_reg_isa_ext(struct kvm_vcpu *vcpu,
> >                                           const struct kvm_one_reg *reg)
> >  {
> > @@ -403,7 +417,7 @@ static int kvm_riscv_vcpu_get_reg_isa_ext(struct kvm_vcpu *vcpu,
> >                 return -EINVAL;
> >
> >         host_isa_ext = kvm_isa_ext_arr[reg_num];
> > -       if (__riscv_isa_extension_available(&vcpu->arch.isa, host_isa_ext))
> > +       if (__riscv_isa_extension_available(vcpu->arch.isa, host_isa_ext))
> >                 reg_val = 1; /* Mark the given extension as available */
> >
> >         if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
> > @@ -437,30 +451,17 @@ static int kvm_riscv_vcpu_set_reg_isa_ext(struct kvm_vcpu *vcpu,
> >         if (!__riscv_isa_extension_available(NULL, host_isa_ext))
> >                 return  -EOPNOTSUPP;
> >
> > -       if (host_isa_ext >= RISCV_ISA_EXT_BASE &&
> > -           host_isa_ext < RISCV_ISA_EXT_MAX) {
> > -               /*
> > -                * Multi-letter ISA extension. Currently there is no provision
> > -                * to enable/disable the multi-letter ISA extensions for guests.
> > -                * Return success if the request is to enable any ISA extension
> > -                * that is available in the hardware.
> > -                * Return -EOPNOTSUPP otherwise.
> > -                */
> > -               if (!reg_val)
> > -                       return -EOPNOTSUPP;
> > -               else
> > -                       return 0;
> > -       }
> > -
> > -       /* Single letter base ISA extension */
> >         if (!vcpu->arch.ran_atleast_once) {
> > +               /* All multi-letter extension and a few single letter extension can be disabled */
> >                 host_isa_ext_mask = BIT_MASK(host_isa_ext);
> > -               if (!reg_val && (host_isa_ext_mask & KVM_RISCV_ISA_DISABLE_ALLOWED))
> > -                       vcpu->arch.isa &= ~host_isa_ext_mask;
> > +               if (!reg_val &&
> > +                  ((host_isa_ext_mask & KVM_RISCV_ISA_DISABLE_ALLOWED) ||
> > +                  ((host_isa_ext >= RISCV_ISA_EXT_BASE) && (host_isa_ext < RISCV_ISA_EXT_MAX))))
> > +                       clear_bit(host_isa_ext, vcpu->arch.isa);
> > +               else if (reg_val == 1 && (host_isa_ext != RISCV_ISA_EXT_h))
> > +                       set_bit(host_isa_ext, vcpu->arch.isa);
> >                 else
> > -                       vcpu->arch.isa |= host_isa_ext_mask;
> > -               vcpu->arch.isa &= riscv_isa_extension_base(NULL);
> > -               vcpu->arch.isa &= KVM_RISCV_ISA_ALLOWED;
> > +                       return -EINVAL;
>
> A slightly more readable version of above sequence can be:
>
>         /* All multi-letter extension and a few single letter
> extension can be disabled */
>         if (host_isa_ext >= RISCV_ISA_EXT_MAX)
>             return -EINVAL;
>         disable_allow_mask = KVM_RISCV_ISA_DISABLE_ALLOWED;
>         if (reg_val == 1)
>             set_bit(host_isa_ext, vcpu->arch.isa);

Shouldn't we ensure that (host_isa_ext != RISCV_ISA_EXT_h) here ?

>         else if (!reg_val && test_bit(host_isa_ext, &disable_allow_mask))
>             clear_bit(host_isa_ext, vcpu->arch.isa);
>         else
>             return -EINVAL;
>
>
> >                 kvm_riscv_vcpu_fp_reset(vcpu);
> >         } else {
> >                 return -EOPNOTSUPP;
> > diff --git a/arch/riscv/kvm/vcpu_fp.c b/arch/riscv/kvm/vcpu_fp.c
> > index d4308c512007..748a8f6a9b5d 100644
> > --- a/arch/riscv/kvm/vcpu_fp.c
> > +++ b/arch/riscv/kvm/vcpu_fp.c
> > @@ -16,12 +16,11 @@
> >  #ifdef CONFIG_FPU
> >  void kvm_riscv_vcpu_fp_reset(struct kvm_vcpu *vcpu)
> >  {
> > -       unsigned long isa = vcpu->arch.isa;
> >         struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
> >
> >         cntx->sstatus &= ~SR_FS;
> > -       if (riscv_isa_extension_available(&isa, f) ||
> > -           riscv_isa_extension_available(&isa, d))
> > +       if (riscv_isa_extension_available(vcpu->arch.isa, f) ||
> > +           riscv_isa_extension_available(vcpu->arch.isa, d))
> >                 cntx->sstatus |= SR_FS_INITIAL;
> >         else
> >                 cntx->sstatus |= SR_FS_OFF;
> > @@ -34,24 +33,24 @@ static void kvm_riscv_vcpu_fp_clean(struct kvm_cpu_context *cntx)
> >  }
> >
> >  void kvm_riscv_vcpu_guest_fp_save(struct kvm_cpu_context *cntx,
> > -                                 unsigned long isa)
> > +                                 unsigned long *isa)
> >  {
> >         if ((cntx->sstatus & SR_FS) == SR_FS_DIRTY) {
> > -               if (riscv_isa_extension_available(&isa, d))
> > +               if (riscv_isa_extension_available(isa, d))
> >                         __kvm_riscv_fp_d_save(cntx);
> > -               else if (riscv_isa_extension_available(&isa, f))
> > +               else if (riscv_isa_extension_available(isa, f))
> >                         __kvm_riscv_fp_f_save(cntx);
> >                 kvm_riscv_vcpu_fp_clean(cntx);
> >         }
> >  }
> >
> >  void kvm_riscv_vcpu_guest_fp_restore(struct kvm_cpu_context *cntx,
> > -                                    unsigned long isa)
> > +                                    unsigned long *isa)
> >  {
> >         if ((cntx->sstatus & SR_FS) != SR_FS_OFF) {
> > -               if (riscv_isa_extension_available(&isa, d))
> > +               if (riscv_isa_extension_available(isa, d))
> >                         __kvm_riscv_fp_d_restore(cntx);
> > -               else if (riscv_isa_extension_available(&isa, f))
> > +               else if (riscv_isa_extension_available(isa, f))
> >                         __kvm_riscv_fp_f_restore(cntx);
> >                 kvm_riscv_vcpu_fp_clean(cntx);
> >         }
> > @@ -80,7 +79,6 @@ int kvm_riscv_vcpu_get_reg_fp(struct kvm_vcpu *vcpu,
> >                               unsigned long rtype)
> >  {
> >         struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
> > -       unsigned long isa = vcpu->arch.isa;
> >         unsigned long __user *uaddr =
> >                         (unsigned long __user *)(unsigned long)reg->addr;
> >         unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > @@ -89,7 +87,7 @@ int kvm_riscv_vcpu_get_reg_fp(struct kvm_vcpu *vcpu,
> >         void *reg_val;
> >
> >         if ((rtype == KVM_REG_RISCV_FP_F) &&
> > -           riscv_isa_extension_available(&isa, f)) {
> > +           riscv_isa_extension_available(vcpu->arch.isa, f)) {
> >                 if (KVM_REG_SIZE(reg->id) != sizeof(u32))
> >                         return -EINVAL;
> >                 if (reg_num == KVM_REG_RISCV_FP_F_REG(fcsr))
> > @@ -100,7 +98,7 @@ int kvm_riscv_vcpu_get_reg_fp(struct kvm_vcpu *vcpu,
> >                 else
> >                         return -EINVAL;
> >         } else if ((rtype == KVM_REG_RISCV_FP_D) &&
> > -                  riscv_isa_extension_available(&isa, d)) {
> > +                  riscv_isa_extension_available(vcpu->arch.isa, d)) {
> >                 if (reg_num == KVM_REG_RISCV_FP_D_REG(fcsr)) {
> >                         if (KVM_REG_SIZE(reg->id) != sizeof(u32))
> >                                 return -EINVAL;
> > @@ -126,7 +124,6 @@ int kvm_riscv_vcpu_set_reg_fp(struct kvm_vcpu *vcpu,
> >                               unsigned long rtype)
> >  {
> >         struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
> > -       unsigned long isa = vcpu->arch.isa;
> >         unsigned long __user *uaddr =
> >                         (unsigned long __user *)(unsigned long)reg->addr;
> >         unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > @@ -135,7 +132,7 @@ int kvm_riscv_vcpu_set_reg_fp(struct kvm_vcpu *vcpu,
> >         void *reg_val;
> >
> >         if ((rtype == KVM_REG_RISCV_FP_F) &&
> > -           riscv_isa_extension_available(&isa, f)) {
> > +           riscv_isa_extension_available(vcpu->arch.isa, f)) {
> >                 if (KVM_REG_SIZE(reg->id) != sizeof(u32))
> >                         return -EINVAL;
> >                 if (reg_num == KVM_REG_RISCV_FP_F_REG(fcsr))
> > @@ -146,7 +143,7 @@ int kvm_riscv_vcpu_set_reg_fp(struct kvm_vcpu *vcpu,
> >                 else
> >                         return -EINVAL;
> >         } else if ((rtype == KVM_REG_RISCV_FP_D) &&
> > -                  riscv_isa_extension_available(&isa, d)) {
> > +                  riscv_isa_extension_available(vcpu->arch.isa, d)) {
> >                 if (reg_num == KVM_REG_RISCV_FP_D_REG(fcsr)) {
> >                         if (KVM_REG_SIZE(reg->id) != sizeof(u32))
> >                                 return -EINVAL;
> > --
> > 2.25.1
> >
>
> Apart from minor comments above, this looks good to me.
>
Thanks.

> I have taken care of the above comments and queued it for 5.20. I
> can certainly modify my queue if you want further changes in this patch.
>
> Thanks,
> Anup



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