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

From: Anup Patel
Date: Mon Jul 04 2022 - 04:47:57 EST

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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.

> 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.

> +};
>
> 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);
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.

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

Next message: Chen-Yu Tsai: "[PATCH] media: mediatek: vcodec: Initialize decoder parameters for each instance"
Previous message: AngeloGioacchino Del Regno: "Re: [PATCH 0/3] clk: mediatek: mt8183: Simplify with mtk_clk_simple_*()"
Next in thread: Atish Kumar Patra: "Re: [PATCH] RISC-V: KVM: Improve ISA extension by using a bitmap"
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